avoid a misconfiguration infinite loop

The virtual type configurations are not supposed to be self‑referential, … but if they ever are this function will spin in an infinite loop.

Author: ergohack

lib/internal/Magento/Framework/ObjectManager/Config/Config.php

@@ -156,6 +156,7 @@ public function isShared($type)
     public function getInstanceType($instanceName)
     {
         while (isset($this->_virtualTypes[$instanceName])) {
+            if ($instanceName == $this->_virtualTypes[$instanceName]) break;
             $instanceName = $this->_virtualTypes[$instanceName];
         }
         return $instanceName;