HTTP requests without leading "/" (e.g. GET ?a=b ...) are not routed to index controller (one with path="/").

How to reproduce:
Create a new Symfony project and configure it to run under a root of any hostname (let it be http://localhost/).
Do not use a browser because majority of them do not produce requests like the one in question. Instead use telnet:

telnet localhost 80
> GET ?a=b HTTP/1.1
> Host: localhost
>

Expected output: welcome page (same as for GET /?a=b ...).
Actual output: "404 Not Found" page.

Reproduced with latest versions of v2.8 and v3.2 but other releases should be affected too.