h264: Reset last_pocs in case of reference or frame number inconsistencies

This prevents faulty increasing of has_b_frames
Should fix Ticket 2062

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit c230af9bccc3cadb373f9007ba14fffb6c2acc75)
Signed-off-by: Jean-Yves Avenard <jyavenard@mythtv.org>
(cherry picked from commit 1c1076385f01619f0d0933f9f4fb8f5d1e80435b)

Conflicts:
	mythtv/external/FFmpeg/libavcodec/h264_refs.c