[FATAL] Executing someone after forcing them to sleep results in the server being laid in eternal rest

[M3739]

Title says all. Mostly. Bug found as of PR #501.

While I was attempting to debug for an unrelated issue, I was messing around as Manti on a map just seeing what it entails and such, and decided to push down a Urist McVulp, force them to sleep, then execute with the psionic knife. This proceeded to cause the client to "halt" rather than freeze, and the server to throw a fatal error. Oddly enough, with the server throwing such an error, the client did not disconnect.

I attempted this again, this time using the captain's sabre and the debug map. While the sabre worked as intended, the psionic knife threw the same fatal error. While I was recording this, thinking it might have been the system not knowing how to handle holy damage, I then discovered it wasn't the psionic knife, nor holy damage, but something else entirely. I do not know enough about the code to figure out exactly why this is happening, but I do know that it is a severe issue that needs correction as soon as possible to ensure nobody can just kill a server on a whim.

So far, after some further testing, I have discovered the following;

• Bug does not occur when target is on a bed, or already damaged.
• Sleeping in any other way, either through chems, or the target willfully sleeping, will not trigger the bug.
• The target MUST be forced to sleep via the interact system, then executed.
• This bug only occurs when executing another player.
• This can be done with something as easy to get as a shiv.

Video is through this streamable link.

Fatal error in question;

[FATL] unhandled: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
   at System.Collections.Generic.Dictionary`2.Enumerator.MoveNext()
   at Robust.Shared.GameObjects.EntityQueryEnumerator`2.MoveNext(EntityUid& uid, TComp1& comp1, TComp2& comp2) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Shared\GameObjects\EntityManager.Components.cs:line 1801
   at Content.Shared.DoAfter.SharedDoAfterSystem.Update(Single frameTime) in C:\Users\M3739\Documents\GitHub\FS-Yesod\Content.Shared\DoAfter\SharedDoAfterSystem.Update.cs:line 23
   at Robust.Shared.GameObjects.EntitySystemManager.TickUpdate(Single frameTime, Boolean noPredictions) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Shared\GameObjects\EntitySystemManager.cs:line 306
   at Robust.Shared.GameObjects.EntityManager.TickUpdate(Single frameTime, Boolean noPredictions, Histogram histogram) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Shared\GameObjects\EntityManager.cs:line 256
   at Robust.Server.GameObjects.ServerEntityManager.TickUpdate(Single frameTime, Boolean noPredictions, Histogram histogram) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\GameObjects\ServerEntityManager.cs:line 195
   at Robust.Server.BaseServer.Update(FrameEventArgs frameEventArgs) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\BaseServer.cs:line 729
   at Robust.Server.BaseServer.<SetupMainLoop>b__66_1(Object sender, FrameEventArgs args) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\BaseServer.cs:line 542
   at Robust.Shared.Timing.GameLoop.Run() in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Shared\Timing\GameLoop.cs:line 235
   at Robust.Server.BaseServer.MainLoop() in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\BaseServer.cs:line 569
   at Robust.Server.Program.ParsedMain(CommandLineArgs args, Boolean contentStart, ServerOptions options) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\Program.cs:line 74
   at Robust.Server.Program.Start(String[] args, ServerOptions options, Boolean contentStart) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\Program.cs:line 42
   at Robust.Server.ContentStart.Start(String[] args) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\ContentStart.cs:line 10
   at Content.Server.Program.Main(String[] args) in C:\Users\M3739\Documents\GitHub\FS-Yesod\Content.Server\Program.cs:line 9
Unhandled exception. System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
   at System.Collections.Generic.Dictionary`2.Enumerator.MoveNext()
   at Robust.Shared.GameObjects.EntityQueryEnumerator`2.MoveNext(EntityUid& uid, TComp1& comp1, TComp2& comp2) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Shared\GameObjects\EntityManager.Components.cs:line 1801
   at Content.Shared.DoAfter.SharedDoAfterSystem.Update(Single frameTime) in C:\Users\M3739\Documents\GitHub\FS-Yesod\Content.Shared\DoAfter\SharedDoAfterSystem.Update.cs:line 23
   at Robust.Shared.GameObjects.EntitySystemManager.TickUpdate(Single frameTime, Boolean noPredictions) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Shared\GameObjects\EntitySystemManager.cs:line 306
   at Robust.Shared.GameObjects.EntityManager.TickUpdate(Single frameTime, Boolean noPredictions, Histogram histogram) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Shared\GameObjects\EntityManager.cs:line 256
   at Robust.Server.GameObjects.ServerEntityManager.TickUpdate(Single frameTime, Boolean noPredictions, Histogram histogram) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\GameObjects\ServerEntityManager.cs:line 195
   at Robust.Server.BaseServer.Update(FrameEventArgs frameEventArgs) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\BaseServer.cs:line 729
   at Robust.Server.BaseServer.<SetupMainLoop>b__66_1(Object sender, FrameEventArgs args) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\BaseServer.cs:line 542
   at Robust.Shared.Timing.GameLoop.Run() in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Shared\Timing\GameLoop.cs:line 235
   at Robust.Server.BaseServer.MainLoop() in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\BaseServer.cs:line 569
   at Robust.Server.Program.ParsedMain(CommandLineArgs args, Boolean contentStart, ServerOptions options) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\Program.cs:line 74
   at Robust.Server.Program.Start(String[] args, ServerOptions options, Boolean contentStart) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\Program.cs:line 42
   at Robust.Server.ContentStart.Start(String[] args) in C:\Users\M3739\Documents\GitHub\FS-Yesod\RobustToolbox\Robust.Server\ContentStart.cs:line 10
   at Content.Server.Program.Main(String[] args) in C:\Users\M3739\Documents\GitHub\FS-Yesod\Content.Server\Program.cs:line 9

[Mnemotechnician]

Not relevant to the weapons used or anything like that; this is just one of the many situations in which a system may remove/add a component from/to an entity while it or another system is iterating over an EntityQueryEnumerator of the same component type. This is a non-critical issue as in release builds the exception will be simply caught and logged.