Bug 14769: Add tests for _thesaurus_info in ControlledIndicators.t

Bug 14769: Add tests for _thesaurus_info in ControlledIndicators.t

Apart from adding tests for this sub, we make the following change
too and support it with a test.

The fallback to $code in the construction
    $thes_mapping{ $code } // $code // '4'
is removed by this patch. When $code is not in $thes_mapping, we cannot
assume that it is a valid code for a biblio indicator. In this case it is
more safe to mark it as 4 (Source not specified).

Test plan:
Run t/Koha/Authority/ControlledIndicators.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>