Handle requests without _route safely in active_for_routes

[javihgil]

Problem

active_for_routes() assumes the current request has a _route attribute.

If a request exists but the route attribute is missing, the helper can behave in a fragile way because the value is used directly in preg_match().

Current evidence

• src/Twig/Extension/ActiveForRoutesExtension.php reads $request->attributes->get('_route')
• the value is then passed into preg_match() without an explicit guard for missing or non-string values

Expected behavior

The helper should return an empty string when the current request does not provide a valid route name.

Suggested work

• guard the _route value before matching
• treat missing or non-string route names as a non-match
• add tests that cover requests without _route