render/drm_format_set: Clean up on union failure

If drm_format_set_extend fails, we need to make sure each wlr_drm_format
is cleaned up together with the formats array. Finish the set to take
care of it.

render/drm_format_set.c

@@ -271,10 +271,9 @@ bool wlr_drm_format_set_union(struct wlr_drm_format_set *dst,
 	}
 
 	// Add both a and b sets into out
-	if (!drm_format_set_extend(&out, a)) {
+	if (!drm_format_set_extend(&out, a) ||
-		return false;
+		!drm_format_set_extend(&out, b)) {
-	}
+		wlr_drm_format_set_finish(&out);
-	if (!drm_format_set_extend(&out, b)) {
 		return false;
 	}