Merge pull request #73 from NicolasCador/patch-1

Undefined array key 0 in Subject select input

contactform.php

@@ -331,7 +331,7 @@ public function getTemplateVarContact()
             $contacts[$one_contact['id_contact']] = $one_contact;
         }
 
-        if (isset($this->customer_thread['id_contact'])) {
+        if (!empty($this->customer_thread['id_contact'])) {
             return [
                 $contacts[$this->customer_thread['id_contact']],
             ];