Bug 20430: (See also bug 19436) Button display depends on wrong server count

Bug 20430: (See also bug 19436) Button display depends on wrong server count

This is a QA follow-up of bug 19436, submitted separately for ease of
backporting it. (The bug was not raised by 19436.)

Obviously, the number of authority servers not biblio servers should
be the key factor for showing or hiding the button for new authority
records via Z39.50/SRU.

Trivial fix.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>