Auto-start session only upon 1st "->visit(...)" method call breaks my test suite

PR #705 from @aik099 breaks my testsuite as I am resizing the Window prior to each scenario.

class FeatureContext extends RawMinkContext
{
    use KernelDictionary;

    /**
     * @BeforeScenario
     */
    public function beforeScenario()
    {
        if ($this->getSession()->getDriver() instanceof Selenium2Driver) {
            $this->getSession()->resizeWindow(1440, 900, 'current');
        }
    }
}

This breaks with the error:

    ┌─ @BeforeScenario # AppBundle\Features\Context\FeatureContext::beforeScenario()
    │
    ╳  Fatal error: Call to a member function window() on null (Behat\Testwork\Call\Exception\FatalThrowableError)
    │

Start with PR #705 and the FeatureContext example, then trace getSession()->getDriver() and resizeWindow(1440, 900, 'current') through Selenium2Driver. Reproduce the failure when resizing occurs before any visit call; done means the @BeforeScenario resize works without the null-window fatal error.