avutil/opt: Check av_parse_video_rate()s return value

Fixes CID1257008
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/opt.c

@@ -1811,8 +1811,10 @@ int av_opt_is_set_to_default(void *obj, const AVOption *o)
         return (w == *(int *)dst) && (h == *((int *)dst+1));
     case AV_OPT_TYPE_VIDEO_RATE:
         q = (AVRational){0, 0};
-        if (o->default_val.str)
-            av_parse_video_rate(&q, o->default_val.str);
+        if (o->default_val.str) {
+            if ((ret = av_parse_video_rate(&q, o->default_val.str)) < 0)
+                return ret;
+        }
         return !av_cmp_q(*(AVRational*)dst, q);
     case AV_OPT_TYPE_COLOR: {
         uint8_t color[4] = {0, 0, 0, 0};