Canonical: prevent possible "Undefined array key" PHP error in redirect_canonical(), if the path or query array keys have gone missing.

This commit checks for the existence of (and re-adds if necessary) the `path` and `query` array keys after the `$redirect` variable has potentially been replaced by a second call to `parse_url()`.

This may happen when redirecting back to the root domain, without any path ('/example/`) or query (`?example=1`) to parse.

Props chrismattix, dhruvang21.

Fixes #63733.

git-svn-id: https://develop.svn.wordpress.org/trunk@60496 602fd350-edb4-49c9-b593-d223f7449a82

Author: JJJ

src/wp-includes/canonical.php

@@ -615,6 +615,14 @@ function redirect_canonical( $requested_url = null, $do_redirect = true ) {
 		unset( $redirect['port'] );
 	}
 
+	// Notice prevention after new parse_url( $redirect_url ) calls
+	if ( ! isset( $redirect['path'] ) ) {
+		$redirect['path'] = '';
+	}
+	if ( ! isset( $redirect['query'] ) ) {
+		$redirect['query'] = '';
+	}
+
 	// Trailing /index.php.
 	$redirect['path'] = preg_replace( '|/' . preg_quote( $wp_rewrite->index, '|' ) . '/*?$|', '/', $redirect['path'] );