Bug 18214: Cannot edit list permissions of a private list

Bug 18214: Cannot edit list permissions of a private list

If you have disabled the pref OpacAllowPublicListCreation, your users are
not able to edit the list permissions for private/shared lists.
For a private list they may only be theoretically relevant, but for a shared
list they are relevant.
Since we do not always know the history of a list (has it been public or
shared, does it contains entries from other users) and therefore permissions
are even relevant for a currently private list, we should just allow editing
these permissions.

Test plan:
[1] Do not yet apply this patch.
[2] Disable OpacAllowPublicListCreation.
[3] Create a private list in OPAC. Edit the list. Verify that you do not
    see the permission combo boxes.
[4] Apply this patch. Edit the list again. Do they appear now?

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Magnus Enger <magnus@libriotech.no>
Works as advertised.