Bug 24052: Catch warning between test 5 and 6

Bug 24052: Catch warning between test 5 and 6

Resolve:
ok 5 - Engine returns error on undefined text
XSLT::Base: Empty String at /usr/share/koha/Koha/XSLT/Base.pm line 214.
ok 6 - Engine returns error on empty string

Test plan:
Run perl Base.t and verify that this warning is no longer printed.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>