Code Modernization: Check the return type of parse_url() on Plugin/Theme Editor screens.

As per the PHP manual:
> If the `component` parameter is omitted, an associative array is returned.
> If the `component` parameter is specified, `parse_url()` returns a string (or an int, in the case of `PHP_URL_PORT`) instead of an array. If the requested component doesn't exist within the given URL, `null` will be returned.

Reference: [https://www.php.net/manual/en/function.parse-url.php#refsect1-function.parse-url-returnvalues PHP Manual: parse_url(): Return Values]

While it is probably unlikely that someone would have a direct link to the plugin/theme editor on their home page or even on someone else's homepage, it is entirely possible for the referrer URL to not have a "path" component.

In PHP 8.1, this would lead to a `basename(): Passing null to parameter #1 ($string) of type string is deprecated` notice.

Changing the logic around and adding validation for the return type value of `parse_url()` prevents that.

Follow-up to [51606], [51622], [51626].

Props jrf, hellofromTonya, SergeyBiryukov.
See #53635.

git-svn-id: https://develop.svn.wordpress.org/trunk@51629 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-admin/plugin-editor.php

@@ -312,10 +312,12 @@
 
 	$excluded_referer_basenames = array( 'plugin-editor.php', 'wp-login.php' );
 
-	if ( $referer && ! in_array( basename( parse_url( $referer, PHP_URL_PATH ) ), $excluded_referer_basenames, true ) ) {
-		$return_url = $referer;
-	} else {
-		$return_url = admin_url( '/' );
+	$return_url = admin_url( '/' );
+	if ( $referer ) {
+		$referer_path = parse_url( $referer, PHP_URL_PATH );
+		if ( is_string( $referer_path ) && ! in_array( basename( $referer_path ), $excluded_referer_basenames, true ) ) {
+			$return_url = $referer;
+		}
 	}
 	?>
 	<div id="file-editor-warning" class="notification-dialog-wrap file-editor-warning hide-if-no-js hidden">

src/wp-admin/theme-editor.php

@@ -343,10 +343,12 @@
 
 	$excluded_referer_basenames = array( 'theme-editor.php', 'wp-login.php' );
 
-	if ( $referer && ! in_array( basename( parse_url( $referer, PHP_URL_PATH ) ), $excluded_referer_basenames, true ) ) {
-		$return_url = $referer;
-	} else {
-		$return_url = admin_url( '/' );
+	$return_url = admin_url( '/' );
+	if ( $referer ) {
+		$referer_path = parse_url( $referer, PHP_URL_PATH );
+		if ( is_string( $referer_path ) && ! in_array( basename( $referer_path ), $excluded_referer_basenames, true ) ) {
+			$return_url = $referer;
+		}
 	}
 	?>
 	<div id="file-editor-warning" class="notification-dialog-wrap file-editor-warning hide-if-no-js hidden">