update: fix mgate

app/Payments/MGate.php

@@ -49,7 +49,7 @@ class MGate {
             'notify_url' => $order['notify_url'],
             'return_url' => $order['return_url']
         ];
-        if ($this->config['mgate_source_currency']) {
+        if (isset($this->config['mgate_source_currency'])) {
             $params['source_currency'] = $this->config['mgate_source_currency'];
         }
         $params['app_id'] = $this->config['mgate_app_id'];