forms: Fix ticket submission if already logged in

If a client is already logged into the client portal and attempts to submit
a new ticket, the ticket will be rejected if the contact-information form
has a required field other than `name` and `email`.

This patch fixes `class Client` so that the user-id is fetched from the
database and made available via the `::getUserId()` method. This was already
corrected in the `develop-next` branch for v1.8.1. The `uid` field is passed
into `Ticket::create()` so the user form validation is bypassed.

This commit should be ignored when merged into the 1.8.1 codebase.