don't fake a 404 for non-ajax requests

[RobertHeim]

When symfony2 is updated to at least 2.4 ( which will take until phpbb 3.2 ( https://www.phpbb.com/community/viewtopic.php?f=461&t=2300491 )
we should use routing-conditions

like this: http://stackoverflow.com/a/21661883/386201
here:

phpbb-ext-topictags/controller/main.php

Lines 295 to 296 in 6152e93

	// TODO: when symfony2 is updated to at least 2.4 add to route:
	// condition: "context.isXmlHttpRequest()" instead of using the helper->error(..., 404)

instead of faking a 404 here:

phpbb-ext-topictags/controller/main.php

Line 307 in 6152e93

return $this->helper->error('No route found for "' . $this->helper->get_current_url() . '"' , 404);