Use legacy method when ownCloud is not yet installed

The new `\OCP\ICertificateManager::getAbsoluteBundlePath` API instantiiates an ownCloud view which makes the installation fail as it queries the DB before it actually is setup. This change uses the old approach again for the case that the installation is not yet setup.

The client service is required for the `.htaccess` effectivity check in the setup. In the future we could move this to a JS based one (as we have for the other setupchecks) so we can get rid of such hacks.

Fixes https://github.com/owncloud/core/issues/21669 which was a regression in master caused by https://github.com/owncloud/core/issues/21336