Refactor user authorization check for a single project to avoid querying all user projects

Currently, even when searching for all authorized issues of *one* project, we run the
`Users#authorized_projects` query (which can be rather slow). This update checks if
we are handling issues of just one project and does the authorization check locally.
It does have the downside of basically repeating the logic of `Users#authorized_projects`
on `Project#authorized_for_user`.