Improve share logic for enforced password & expiry date

Improve share logic for enforced password & expiry date

* It's possible for the admin to enforce and expiry date after, some
 shares have been created. This commit makes possible to update the
 share with the new admin constraints.

* This commit would users to modify enforced expiry to anything within
 range and less than the enforced limit in the pre-create dialog for public
 shares.

* This commit fixes, unable to update share without updating password.

Signed-off-by: fenn-cs <fenn25.fn@gmail.com>