h264: skip error concealment when SPS and slices are mismatching

Fixes out of array accesses

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/h264.c

@@ -2367,7 +2367,7 @@ static int field_end(H264Context *h, int in_setup)
      * past end by one (callers fault) and resync_mb_y != 0
      * causes problems for the first MB line, too.
      */
-    if (!FIELD_PICTURE && h->current_slice)
+    if (!FIELD_PICTURE && h->current_slice && !h->sps.new)
         ff_er_frame_end(s);
 
     ff_MPV_frame_end(s);