fix: Valid JSON response for already handled requests

[svrakitin]

Related issue

Closes #2515

Proposed changes

• Add missing returns to avoid writing response twice when getting requests.
• Add missing tests to check that response is valid

Checklist

• I have read the contributing guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security. vulnerability, I
  confirm that I got green light (please contact
  security@ory.sh) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further comments

I noticed that we do not expose client on logout requests, but it seems to be fixed by #2483

[aeneasr]

Thank you!