Fix sync failure if no movies/tvshows in library

Fix tvshow sync, was referencing 'tvshow' ky directly off of xbmc json
request, it behaves like the movie sync code now.
Check for empty results when getting movie/tvshows from xbmc json
request.
Check for empty result prior to actually performing a sync, and abort if
it is empty.
Merge pull request #43 from nate1280/library_empty_fix

Fix sync failure if no movies/tvshows in library