check first if request and response are indeed objects

fixes race condition

since i use printResponse as a AfterScenario hook information why a call was not working:
```
    /**
	 * catch and show errors
	 *
	 * @param AfterScenarioScope $scope
	 *
	 * @AfterScenario
	 */
	public function catchErrors(AfterScenarioScope $scope)
	{
		if ($scope->getTestResult()->isPassed()) {
			return;
		}

		$this->printResponse();
	}
```