Fix no items dropped by boss if one player dies

[abrenneke]

Fixes #78 - A dead player has no body so there's a NullReferenceException. This check is present elsewhere in the file, just seems to have been forgotten here.

[buzzcut-s]

Hey @abrenneke, do you think you can provide a pre-built dll with this fix? Would appreciate it a lot, thanks!

[abrenneke]

@buzzcut-s only if you don't mind if the Classic Items and Dronemeld integrations are disabled - I was unsuccessful in compiling this with those external mods: TinkersSatchel.zip