…ng to use it (gsdevme)

This PR was submitted for the 2.8 branch but it was merged into the 2.7 branch instead (closes #23238).

Discussion
----------

[Security] ensure the 'route' index is set before attempting to use it

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

```
                // matching a request is more powerful than matching a URL path + context, so try that first
                if ($this->urlMatcher instanceof RequestMatcherInterface) {
                    $parameters = $this->urlMatcher->matchRequest($request);
                } else {
                    $parameters = $this->urlMatcher->match($request->getPathInfo());
                }

                return $path === $parameters['_route'];
```
Hi the issue here is the code is assuming a `_route` has been returned from the `match()` method.. however there is nothing to suggest that is always the case. For example if I just want to return a controller that is perhaps not added as an actual route I can & it works.. Although this will generate a notice warning.

**In terms of what happens if the `_route` is not defined should it return `false?` or actually  perform a similar condition as `return $path === rawurldecode($request->getPathInfo());` **

I have an implementation of a router that is just returning a controller path and its arguments without a `_route` which works aside from this notice.

Commits
-------

7ae578c fix(security): ensure the 'route' index is set before attempting to use it