Fixes a logger related crash.

Since we use a stream writer, which stores a reference to a file
resource, we need to avoid storing a reference to the cache object in
the store class, since it is saved in session.

Erfurt/Store.php

@@ -1763,10 +1763,7 @@ private function _getTransitiveClosure($modelIri, $property, $startResources, $i
      */
     protected function _getQueryLogger()
     {
-        if (null === $this->_queryLogger) {
-            $this->_queryLogger =  Erfurt_App::getInstance()->getLog('queries');
-        }
-        return $this->_queryLogger;
+        return $this->_queryLogger =  Erfurt_App::getInstance()->getLog('queries');
     }
 
     /**
@@ -1776,9 +1773,6 @@ protected function _getQueryLogger()
      */
     protected function _getErfurtLogger()
     {
-        if (null === $this->_erfurtLogger) {
-            $this->_erfurtLogger =  Erfurt_App::getInstance()->getLog('erfurt');
-        }
-        return $this->_erfurtLogger;
+        return $this->_erfurtLogger =  Erfurt_App::getInstance()->getLog('erfurt');
     }
 }