MDL-45660 question statistics: fix regression added by MDL-44981.

Also, make comparison more robust.

question/classes/statistics/responses/analysis_for_actual_response.php

@@ -84,7 +84,7 @@ class analysis_for_actual_response {
     }
 
     public function response_matches($response) {
-        return $response == $this->response;
+        return (string)$response === (string)$this->response;
     }
 
     /**

question/classes/statistics/responses/analysis_for_class.php

@@ -107,7 +107,7 @@ class analysis_for_class {
             return true;
         } else if (count($this->actualresponses) == 1) {
             $onlyactualresponse = reset($this->actualresponses);
-            return (string)$onlyactualresponse != $this->modelresponse;
+            return !$onlyactualresponse->response_matches($this->modelresponse);
         }
         return false;
     }