Move trusted domain check to init()

handleRequest() is not called from remote.php or public.php which made these files party available but all included apps in there produced errors.

As the expected behaviour is anyways that a trusted domain warning is shown I moved this to init()

Fixes https://github.com/owncloud/core/issues/10064
Merge pull request #10889 from owncloud/moveTrustedDomainCheck

Move trusted domain check to init()