dashdemux: reworked gst_dash_demux_get_buffering_time() to return the effective buffering time
dashdemux: reworked gst_dash_demux_get_buffering_time() to return the effective buffering time

do not assume the Fragment duration is constant

Orange-OpenSource/gstdashdemux,Orange-OpenSource/gstdashdemux,Orange-OpenSource/gstdashdemux