Prevent array index out of bounds in DVDDemuxVobsub.h

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/1549fc8f6
Zero out DVDVideoPicture struct after resetting the video codec

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/c4b868e93
Prevent the Progress dialog from being activated a second time

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/73482a7c7
Clear the directory cache subpath correctly

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/f45ce6a51
Fix deadlock when airplaying pictures

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/98c4f579b
Handle Redirect in Playlist creation

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/e4c553202
Don't expose GL types to nonGL systems

cherry-picked from
https://github.com/plexinc/plex-home-theater-public/e09d2fa89