gst/mpegaudioparse/gstmpegaudioparse.c: Try a bit harder to get valid timestamps...

gst/mpegaudioparse/gstmpegaudioparse.c: Try a bit harder to get valid timestamps, especially if upstream gives us one...

Original commit message from CVS:
* gst/mpegaudioparse/gstmpegaudioparse.c:
(gst_mp3parse_emit_frame), (gst_mp3parse_chain):
Try a bit harder to get valid timestamps, especially if upstream
gives us one and we are at the first frame or resyncing.
Return UNEXPECTED if we get a valid timestamp that is outside of
our configured segment. After all changes done so far this doesn't
seem to cause any regression, please test.