error_resilience: assert that unsupported B frame interpolation isnt used with h264

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/error_resilience.c

@@ -1186,6 +1186,7 @@ void ff_er_frame_end(MpegEncContext *s)
                     int time_pp = s->pp_time;
                     int time_pb = s->pb_time;
 
+                    av_assert0(s->avctx->codec_id != AV_CODEC_ID_H264);
                     ff_thread_await_progress(&s->next_picture_ptr->f, mb_y, 0);
                     s->mv[0][0][0] = s->next_picture.f.motion_val[0][xy][0] *  time_pb            / time_pp;
                     s->mv[0][0][1] = s->next_picture.f.motion_val[0][xy][1] *  time_pb            / time_pp;