fix: null password handling in entry control logic

[st3iny]

Fix #448
Fix nextcloud/user_saml#709

BeforeUserLoggedInEvent is allowed to contain no password (string|null). However, the entry control logic fails if the password is null, because it always expects a string.

public function entryControl(string $loginName, string $password) {}

I fixed this by also allowing null for the password. There is only one implementation of the IEntryControl interface in this app and it doesn't even make use of the password param so this should be safe change.

There don't seem to be any other implementations of this interface outside this app (source: GitHub search for IEntryControl).

[st3iny]

/backport to stable26

[solracsf]

Can this be backported to 25?
nextcloud/user_saml#715

[st3iny]

/backport to stable25