adaptivedemux: Support period change in live playlist

Regardless of LIVE or VOD, "a manifest has next period but
currently EOSed" state is meaning that it's time to advance period.

Previous behavior of adpativedemux, however, was able to period
advancing only for VOD case, since the adaptivedemux tried to
update and wait new manifest without respecting existence of the next period.

https://bugzilla.gnome.org/show_bug.cgi?id=781183
1 file changed