ext/amrnb/: Sortof first quick cleanup of all this mess...

ext/amrnb/: Sortof first quick cleanup of all this mess...

Original commit message from CVS:
* ext/amrnb/amrnbdec.c: (gst_amrnbdec_event), (gst_amrnbdec_chain):
* ext/amrnb/amrnbparse.c: (gst_amrnbparse_init),
(gst_amrnbparse_sink_event), (gst_amrnbparse_chain),
(gst_amrnbparse_sink_activate), (gst_amrnbparse_state_change):
* ext/amrnb/amrnbparse.h:
Sortof first quick cleanup of all this mess...
Don't crap out on empty and invalid FTs but treat them as
empty packets, the decoder handles them fine.
Fixes #342222.