Fix saving NULL value

This reverts commit ed130065.

Conflicts:
	adminer/drivers/mongo.inc.php
	adminer/include/functions.inc.php

adminer/include/driver.inc.php

@@ -10,14 +10,6 @@
 		$this->_conn = $connection;
 	}
 	
-	/** Quote a SQL string or null value
-	* @param string
-	* @return string
-	*/
-	function quote($value) {
-		return ($value === null ? "NULL" : $this->_conn->quote($value));
-	}
-	
 	/** Select data from table
 	* @param string
 	* @param array result of $adminer->selectColumnsProcess()[0]