check for password during update public link

[micbar]

Bugfix: Fix public links with enforced password

Fix the public link update operation in the case that a password is enforced.

[kobergj]

confused

[micbar]

confused

I was too at the beginning. Let me explain.

From the backend side, things always look different.

In the web frontend you have the following situation:

1. You create a link. During that, you cannot specify permissions, it just uses the default and no password
2. You want to change the permissions to "Editor". Now the Frontend side validation kicks in ans says: "hey, that doesn't work without a password!" and prompts a password. You provide one and violà, we have a request that updates the permissions and the password together. IMO this makes sense.