Merge commit 'b69183f6'

* commit 'b69183f6':
  nutenc: check for negative index rather than assert

Conflicts:
	libavformat/nutenc.c

Not merged, the assert is correct
Merged-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/nutenc.c

@@ -1119,6 +1119,7 @@ static int nut_write_packet(AVFormatContext *s, AVPacket *pkt)
         }
     }
     av_assert0(frame_code != -1);
+
     fc           = &nut->frame_code[frame_code];
     flags        = fc->flags;
     needed_flags = get_needed_flags(nut, nus, fc, pkt);