The period start information, calculated in gst_mpd_client_setup_media_presentation
function is stored in stream_period->start. The information read from
xml file and stored in stream_period->period->start is not changed.
If the xml file does not contain the period start information,
stream_period->period->start will be -1.
The function gst_mpd_client_get_next_segment_availability_end_time wants to
use period start time, but incorrectly uses stream_period->period->start
(value from xml file, which could be -1) instead of stream_period->start
(computed value)
https://bugzilla.gnome.org/show_bug.cgi?id=751465
93f08347de