Ensure SelectLimit $nrows and`$offset parameters are integers

The same is done (at least for `$nrows`) in the `SelectLimit` method of `Adodb/adodb.inc.php`.

This lowers the risk of SQL injection.

Fixes ADOdb#311

(cherry picked from commit 7d43989)

drivers/adodb-pdo_mysql.inc.php

@@ -201,6 +201,8 @@ function SelectDB($dbName)
 	// parameters use PostgreSQL convention, not MySQL
 	function SelectLimit($sql, $nrows=-1, $offset=-1, $inputarr=false, $secs=0)
 	{
+		$nrows = (int) $nrows;
+		$offset = (int) $offset;		
 		$offsetStr =($offset>=0) ? "$offset," : '';
 		// jason judge, see http://phplens.com/lens/lensforum/msgs.php?id=9220
 		if ($nrows < 0) {