[2/4] (Try2) msi/tests: Add empty dir test for the DrLocator part of the AppSearch action.

[Nicolas Le Cam]

Try2: Move relative to absolute path logic into a helper function and
added a comment to explain why it's needed, as suggested by James.

This patch adds a test to demonstrate current wrong behaviour in case of
an empty path, it is basically there to validate last patch of the
series that change relative path test behaviour (i.e. expected values),
as it seems it was rejected because it wasn't backed up by a previous
test.

--
Nicolas Le Cam