Fix logic in fallback ringtone handling

The existing code would only play a fallback ringtone if the requested
ringtone was one of the three ringtone uris that are defined by settings,
and it wasn't set to "silent".
Now it also plays the fallback for custom ringtone uris.

b/10891718

Change-Id: I79c2298c6497165e6845b98532cce0855347e50b