integer conversion added

Author: Webklex

src/IMAP/Message.php

@@ -450,6 +450,7 @@ protected function fetchAttachment($structure, $partNumber){
      * @return $this
      */
     public function setFetchOption($option){
+        $option = (integer)$option;
         if(is_long($option) == true){
             $this->fetch_options = $option;
         }elseif(is_null($option) == true){