adaptivedemux: Retry downloading a fragment immediately if any in live streaming

At the moment that demux is waiting manifest update, the target sequence
of fragment was advanced already. So, checking stream_has_next_fragment()
means looking for the next fragment of target fragment.
This might cause unexpected buffering if each fragment has
large duration and manifest is listing only limited number of fragments.

https://bugzilla.gnome.org/show_bug.cgi?id=780494
1 file changed