When displaying the repo home view, do not redirect to unit types that
can't be defaults (which, at the moment, are the external wiki and issue
tracker unit types).
If we'd redirect to those, that would mean that a repository with the
Code unit disabled, and an external issue tracker would immediately
redirect to the external issue tracker, making it harder to reach other,
non-external units of the repo.
Fixes#1965.
Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>
(cherry picked from commit 44078e5460)
(cherry picked from commit 1868dec2e4)
c3a8e98870