Code Modernization: Return an empty string from `wpdb::_real_escape()` if a non-scalar value is passed.

This avoids a fatal error on PHP 8 caused by passing a non-string value to ` mysqli_real_escape_string()`, and maintains the current behaviour.

See #50913, #50639.
Built from https://develop.svn.wordpress.org/trunk@48980


git-svn-id: http://core.svn.wordpress.org/trunk@48742 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6-alpha-48979';
+$wp_version = '5.6-alpha-48980';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-includes/wp-db.php

@@ -1159,6 +1159,10 @@ class wpdb {
 	 * @return string Escaped string.
 	 */
 	function _real_escape( $string ) {
+		if ( ! is_scalar( $string ) && ! is_null( $string ) ) {
+			return '';
+		}
+
 		if ( $this->dbh ) {
 			if ( $this->use_mysqli ) {
 				$escaped = mysqli_real_escape_string( $this->dbh, $string );