[FrameworkBundle] fixed requirement of the _controller palceholder for the proxy route (closes #6783)

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #6783
| License       | MIT
| Doc PR        | n/a