Fix error from reddening calculation

[hover2pi]

With dustmaps removed as a dependency, running an SED now shows an error multiple times (though the calculation seems to complete).

Modify the reddening lookup so it can fail gracefully and just set it to 0.

[SherelynA]

Huh, that is what the error means, I have been seeing it but I wasn't sure where it was coming from @hover2pi.