Correctly set request context before matching routes

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | ---
| Fixed tickets | ---
| Refs tickets  | ---
| License       | MIT
| Doc PR        | ---

(cannot be done via EventListener on KERNEL_REQUEST, as the method is called in Core::init() and therefore before Symfony)