Fixed invalid free on picture_NewFromFormat failure in subpicture_region_New.

src/video_output/vout_subpictures.c

@@ -818,7 +818,7 @@ subpicture_region_t *subpicture_region_New( const video_format_t *p_fmt )
     p_region->p_picture = picture_NewFromFormat( p_fmt );
     if( !p_region->p_picture )
     {
-        free( p_fmt->p_palette );
+        free( p_region->fmt.p_palette );
         free( p_region );
         return NULL;
     }