ffmpeg_filter: fix leak on error

Fixes: CID1005311
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg_filter.c

@@ -318,17 +318,18 @@ static int configure_output_video_filter(FilterGraph *fg, OutputFilter *ofilter,
         AVFilterContext *filter;
         snprintf(name, sizeof(name), "pixel format for output stream %d:%d",
                  ost->file_index, ost->index);
-        if ((ret = avfilter_graph_create_filter(&filter,
+        ret = avfilter_graph_create_filter(&filter,
                                                 avfilter_get_by_name("format"),
                                                 "format", pix_fmts, NULL,
-                                                fg->graph)) < 0)
+                                                fg->graph);
+        av_freep(&pix_fmts);
+        if (ret < 0)
             return ret;
         if ((ret = avfilter_link(last_filter, pad_idx, filter, 0)) < 0)
             return ret;
 
         last_filter = filter;
         pad_idx     = 0;
-        av_freep(&pix_fmts);
     }
 
     if (ost->frame_rate.num && 0) {