Revert and change prior check to assertion

Author: Girgias

ext/pdo_mysql/pdo_mysql.c

@@ -63,13 +63,13 @@ static MYSQLND * pdo_mysql_convert_zv_to_mysqlnd(zval * zv)
 	if (Z_TYPE_P(zv) == IS_OBJECT && instanceof_function(Z_OBJCE_P(zv), php_pdo_get_dbh_ce())) {
 		pdo_dbh_t * dbh = Z_PDO_DBH_P(zv);
 
-		if (!dbh) {
-			php_error_docref(NULL, E_WARNING, "Failed to retrieve handle from object store");
+		ZEND_ASSERT(dbh);
+
+		if (dbh->driver != &pdo_mysql_driver) {
+			php_error_docref(NULL, E_WARNING, "Provided PDO instance is not using MySQL but %s", dbh->driver->driver_name);
 			return NULL;
 		}
 
-		ZEND_ASSERT(dbh->driver == &pdo_mysql_driver);
-
 		return ((pdo_mysql_db_handle *)dbh->driver_data)->server;
 	}
 	return NULL;