Bug 17866: [QA Follow-up] Reword message for missing email address

Bug 17866: [QA Follow-up] Reword message for missing email address

See BZ, comment 14 from Jonathan.

In the exceptional case that branch email address and fallback, i.e.
preference KohaAdminEmailAddress, are both empty or not valid, the error
message should reflect that (of course :)

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Removed branch email and KohaAdminEmailAddress.
Followed the test plan of the first patch and saw the alert.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>