Login and Registration: Fix "passing null to non-nullable" deprecation for authorize_application error message.

If there is no URL query in the `$_GET['redirect_to'], `wp_parse_url()` will return `null`. Passing `null` to `parse_str()` results in a PHP 8.1 deprecation notice
{{{
Deprecated: parse_str(): Passing null to parameter #1 ($string) of type string is deprecated
}}}

This commit:
- Fixes the deprecation notice.
- Skips doing the `parse_str()` when there's no URL query.
- Provides a micro-optimization performance boost.

Follow-up to [49109].

Props jrf, hellofromTonya, BinaryKitten.
See #53635.

git-svn-id: https://develop.svn.wordpress.org/trunk@51829 602fd350-edb4-49c9-b593-d223f7449a82

Author: hellofromtonya

src/wp-login.php

@@ -1267,7 +1267,10 @@ function wp_login_viewport_meta() {
 				$errors->add( 'enter_recovery_mode', __( 'Recovery Mode Initialized. Please log in to continue.' ), 'message' );
 			} elseif ( isset( $_GET['redirect_to'] ) && false !== strpos( $_GET['redirect_to'], 'wp-admin/authorize-application.php' ) ) {
 				$query_component = wp_parse_url( $_GET['redirect_to'], PHP_URL_QUERY );
-				parse_str( $query_component, $query );
+				$query           = array();
+				if ( $query_component ) {
+					parse_str( $query_component, $query );
+				}
 
 				if ( ! empty( $query['app_name'] ) ) {
 					/* translators: 1: Website name, 2: Application name. */