Fix T15762. There's a complex interaction with project's AutoCapability requiring the membership info
to be already loaded, and the Mention rule assuming any project is fully loaded before trying to check
permissions.

As far as I can tell, the "contextObject" is currently used only to make the mention handle gray if
the mentioned user can't see it.

Load a Project's hovercard that @mentions a user that can't see the project - no crash.