baseparse: Make sure DISCONT flags are properly propagated
baseparse: Make sure DISCONT flags are properly propagated

If we drop a frame that contained a discontinuity, we must remember
that for the next frame that *will* be pushed downstream.

https://bugzilla.gnome.org/show_bug.cgi?id=766795

StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer