Query: Correct the "matched rule" condition in WP::parse_request().

The `WP::$matched_rule` property is always set now, so we should check that it's not empty instead.

Follow-up to [52804].

See #55222.
Built from https://develop.svn.wordpress.org/trunk@52805


git-svn-id: http://core.svn.wordpress.org/trunk@52394 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp.php

@@ -252,7 +252,7 @@ class WP {
 				}
 			}
 
-			if ( isset( $this->matched_rule ) ) {
+			if ( ! empty( $this->matched_rule ) ) {
 				// Trim the query of everything up to the '?'.
 				$query = preg_replace( '!^.+\?!', '', $query );