MAGETWO-69365: Fix undefined offset notice when no order states are set #4903

 - Merge Pull Request #4903 from adragus-inviqa/magento2:patch-3

Author: vrann

app/code/Magento/Sales/Model/Order/Config.php

@@ -250,7 +250,10 @@ public function getInvisibleOnFrontStatuses()
      */
     protected function _getStatuses($visibility)
     {
-        if ($this->statuses == null) {
+        if ($this->statuses === null) {
+            
+            $this->statuses = [ true => [], false => [] ];
+            
             foreach ($this->_getCollection() as $item) {
                 $visible = (bool) $item->getData('visible_on_front');
                 $this->statuses[$visible][] = $item->getData('status');