Bug 15339: [QA Follow-up] Add a warning too when source is not supplied

Bug 15339: [QA Follow-up] Add a warning too when source is not supplied

When you do not supply a source and add a few wrong parameters, you
would not be warned. Because build simply returns undef.
Adding a carp and a test for that situation too.

Note: In the earlier subtest 'trivial tests' build was called without
source. This now generates a warning. We just catch if there is a warning
and test the actual warning itself later on.

Test plan:
Run t/db_dependent/TestBuilder.t

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