Mark mHandshakeComplete as volatile.

Fixes an issue where the handshake can complete in one thread and
mHandshakeComplete is set to true, but then callbacks do work in
another thread and mHandshakeComplete is still false.
Fix a crash when musicfolder items do not have URLs.

At least one server in the wild does not return URLs for musicfolder
queries when asked.
Fix an NPE in SqueezeService.getCurrentPlaylist().

- Check for null playerState, return null in that case.

- Note that the currentPlaylist is normally a string, so if
  getCurrentPlaylist returns null it indicates a special condition.

- Use this in CurrentPlaylistActivity to affect the visibility of
  menu items for managing the playlist. Make sure the options menu
  is regenerated when player information changes.

- Add annotations for nullity in relevant locations.
Fix NPE in SqueezeService.isPlaying().
Save the LMS version number to Crashlytics if there's a crash.
Prepare for release 1.2.2.
Merge branch 'release-1.2.2' into develop