fix: editing name of object overwrites custom image

[nftchance]

#246 introduces a new bug I had not planned for where the name is changed, and then we generate a new image for them.

If they are using an auto-generated image, we want to update the image any time they update the name; however, if they are not using an auto-generated image, then we need to leave it so that we do not overwrite custom images a user uploads.

[nftchance]

This is actually quite simple to fix with a little lock if we are on a form of an object that already exists. When the lock is checked, don't generate a new image.