svq3: Check for any negative return value from ff_h264_check_intra_pred_mode

Also pass on any returned error code.

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/svq3.c

@@ -652,9 +652,9 @@ static int svq3_decode_mb(SVQ3Context *s, unsigned int mb_type)
         dir = i_mb_type_info[mb_type - 8].pred_mode;
         dir = (dir >> 1) ^ 3 * (dir & 1) ^ 1;
 
-        if ((h->intra16x16_pred_mode = ff_h264_check_intra_pred_mode(h, dir, 0)) == -1) {
-            av_log(h->avctx, AV_LOG_ERROR, "check_intra_pred_mode = -1\n");
-            return -1;
+        if ((h->intra16x16_pred_mode = ff_h264_check_intra_pred_mode(h, dir, 0)) < 0) {
+            av_log(h->avctx, AV_LOG_ERROR, "ff_h264_check_intra_pred_mode < 0\n");
+            return h->intra16x16_pred_mode;
         }
 
         cbp     = i_mb_type_info[mb_type - 8].cbp;