The rationale being that the empty string is not a valid path component.
[ChangeLog][QtCore][QDir] QDir::relativeFilePath() now returns "."
instead of an empty string if the given path is the same as the
directory.
Change-Id: Ibcf31904b2ae5edf5639d4c2e5ba234365d347fd
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>