Bug 16012: Restore the ability to edit default authority type

Bug 16012: Restore the ability to edit default authority type

Bug 15380 introduced a regression on the authority types admin page: the
default authority type (authtypecode="") is no longer editable.

Test plan:
Edit the authority type to update the summary
=> Without this patch you will get the "add a new authority type" form
=> With this patch applied, the correct behavior will be restored

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Brendan Gallagher brendan@bywatersolutions.com