Workaround for QFileInfo::isBundle().

For some reason the former code did not work anyore as expected,
the issue seems to be in QFileInfo::isBundle or how we used it.
To not depend on a possible fix in Qt, we now always resolve the
path before we ask QFileInfo if it is a bundle.

Fixes also the behavior change introduced in cead4555. On OSX,
we get the .dat file passed that's inside the bundle, still we
need to read the data from a .dat file that's located beside
the app bundle...

Change-Id: Idaa7adc6fbad6bd8e9ce90c383b34ea51fe40e8f
Reviewed-by: Kai Koehne <kai.koehne@digia.com>