I18N: Prevent PHP warning in WP_Textdomain_Registry.

Prevents a warning upon cache invalidation after language pack updates if the arguments don’t have the expected format.

Follow-up to [57287], [57290], [57298], [57299].

See #58919.

git-svn-id: https://develop.svn.wordpress.org/trunk@57303 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-textdomain-registry.php

@@ -228,7 +228,11 @@ public function get_language_files_from_path( $path ) {
 	 * @return void
 	 */
 	public function invalidate_mo_files_cache( $upgrader, $hook_extra ) {
-		if ( 'translation' !== $hook_extra['type'] || array() === $hook_extra['translations'] ) {
+		if (
+			! isset( $hook_extra['type'] ) ||
+			'translation' !== $hook_extra['type'] ||
+			array() === $hook_extra['translations']
+		) {
 			return;
 		}