replaced loop exit with a thrown exception

Author: John Robertson

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

@@ -152,11 +152,17 @@ public function isShared($type)
      *
      * @param string $instanceName
      * @return mixed
+     * @throws \LogicException
      */
     public function getInstanceType($instanceName)
     {
         while (isset($this->_virtualTypes[$instanceName])) {
-            if ($instanceName == $this->_virtualTypes[$instanceName]) break;
+            if ($instanceName == $this->_virtualTypes[$instanceName]) {
+                throw new \LogicException(
+                    'unsupported self-referencing virutal type: '
+                    .$instanceName
+                );
+            }
             $instanceName = $this->_virtualTypes[$instanceName];
         }
         return $instanceName;