rv10: Reject slices that does not have the same type as the first one

This prevents crashes with some corrupted bitstreams.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/rv10.c

@@ -531,6 +531,11 @@ static int rv10_decode_packet(AVCodecContext *avctx,
         if(MPV_frame_start(s, avctx) < 0)
             return -1;
         ff_er_frame_start(s);
+    } else {
+        if (s->current_picture_ptr->f.pict_type != s->pict_type) {
+            av_log(s->avctx, AV_LOG_ERROR, "Slice type mismatch\n");
+            return -1;
+        }
     }
 
     av_dlog(avctx, "qscale=%d\n", s->qscale);