ExternalTicketNumberRecognition produces errors

If I configure ExternalTicketNumberRecognition on a system, with a fairly
standard configuration, I see this in the log file:

~~~~
Mon Jun 30 21:05:27 2014        error   OTRS-otrs.UnitTest-08   Execute Run()
of PostFilterModule
Kernel::System::PostMaster::Filter::FollowUpArticleTypeCheck not successfully!
~~~~

This also happens after I run the unit tests for
ExternalTicketNumberRecognition.

  perl bin/otrs.UnitTest.pl -n ExternalTicketNumberRecognition

I found it to be caused by the changes introduced in bug#10182
http://bugs.otrs.org/show_bug.cgi?id=10182
and the fix is trivial. Fix with unit test attached!

Fixes bug http://bugs.otrs.org/show_bug.cgi?id=10601