Fixing a crash when removing a non-existant badge from a playlist.

This addresses #731.

A crash was occurring when a user attempted to remove a badge from a playlist when that badge no longer existed in the playlist (or, conceivably, never did).  The most obvious way for this to happen that I could repro was having two browser windows open to the playlist page, and deleting the badge in both windows.

I initially treated this as an error condition and displayed an error to the user when this happened, but thought better of it and figured that they don't really need to know about it since the end result is what they want:  The badge is gone from their playlist.  I can change this behavior if desired, though.

There was also a second crash that occurred whenever any error at all was encountered on playlist delete request.  This has also been fixed.