Selenium Testing: no warning when subject is empty

[bschmalhofer]

This happens in scripts/test/Selenium/Agent/AgentTicketCompose.t.
The tests expects a warning about an empty subject, but that message is not visible. It is not obvious what the correct behavior ist.
The test dies when the message is not seen.
The expected message is:

my $Message = 'Article subject will be empty if the subject contains only the ticket hook!';

Marking the failure as TODO for now.