avfilter/vf_format: Check pix_fmts before dereferencing it

Fixes CID1224286
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/vf_format.c

@@ -60,6 +60,9 @@ static av_cold int init(AVFilterContext *ctx)
     int i;
     int ret;
 
+    if (!s->pix_fmts)
+        return AVERROR(EINVAL);
+
     /* count the formats */
     cur = s->pix_fmts;
     while ((cur = strchr(cur, '|'))) {
@@ -72,9 +75,6 @@ static av_cold int init(AVFilterContext *ctx)
     if (!s->formats)
         return AVERROR(ENOMEM);
 
-    if (!s->pix_fmts)
-        return AVERROR(EINVAL);
-
     /* parse the list of formats */
     cur = s->pix_fmts;
     for (i = 0; i < nb_formats; i++) {