Always load authentication apps

The current code path may trigger situations where the LDAP application is not yet loaded and thus problems with the authentication appeared.

In previous versions of ownCloud the authentication mechanism manually loaded these apps which is why this affects ownCloud 8 and master only for my knowledge. (certainly not 6, maybe 7)

Backport to 8 might be something to consider.

Fixes https://github.com/owncloud/core/issues/14469