Fix paths for install script and uncompression
When writing a GHNS implementation where uncompression was set to archive the targeted path was returned.
Because the size was 2 installedFiles.size() == 1
failed. And the targeted path is a very bad fallback,
because this only contains the path in our knsrc file.
So the information into which directory it was uncompressed was not available.
With this we get the path which contains the correct path to the extracted dir and we don't need to mess with internals ;-).
Also the path contained a double slash (this is debugging output):
PS: This might also allow us to get rid of the duplicate uncompression logic in the dolphin installer.