Fix QUrl::topLevelDomain(QUrl::FullyDecoded)

qt_ACE_do(".co.uk") was returning an empty string because of the
leading dot. Allow leading dots from topLevelDomain, but not from
other calls.

Change-Id: I757d9960708e205d30554cd2bbcf618c8624792b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>