hlsdemux: check sequence number as spec defined
Submitted by Jun Xie
Link to original bug (#791981)
Description
#quoted from hls spec:
6.2.2. Live Playlists
Media Segments MUST be removed from the Playlist file in the order
that they appear in the Playlist; otherwise, client playback can
malfunction.
6.3.4. Reloading the Media Playlist File
After reloading a Media Playlist, the client SHOULD verify that each
Media Segment in it has the same URI (and byte range, if specified)
as the Media Segment with the same Media Sequence Number in the
previous Media Playlist. It SHOULD halt playback if it does not, as
this normally indicates a server error.