fftools/ffmpeg_filter: fix leak of AVIOContext in read_binary()

It was only being freed on failure.

Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: James Almer <jamrial@gmail.com>

fftools/ffmpeg_filter.c

@@ -408,11 +408,13 @@ static int read_binary(const char *path, uint8_t **data, int *len)
 
     *len = fsize;
 
-    return 0;
+    ret = 0;
 fail:
     avio_close(io);
+    if (ret < 0) {
         av_freep(data);
         *len = 0;
+    }
     return ret;
 }