video_filter: scene: fix usage when config_GetUserDir returns NULL

The snapshot cannot be created so the filter cannot be used.

modules/video_filter/scene.c

@@ -194,6 +194,16 @@ static int Create( filter_t *p_filter )
     if( p_sys->psz_path == NULL )
         p_sys->psz_path = config_GetUserDir( VLC_PICTURES_DIR );
 
+    if (unlikely(p_sys->psz_path == NULL))
+    {
+        msg_Err( p_filter, "could not create snapshot: no directory" );
+        image_HandlerDelete( p_sys->p_image );
+        free( p_sys->psz_prefix );
+        free( p_sys->psz_format );
+        free( p_sys );
+        return VLC_EGENERIC;
+    }
+
     static const struct vlc_filter_operations filter_ops =
     {
         .filter_video = Filter, .close = Destroy,