KWSys: Fix SystemTools::MakeDirectory after recent cleanup

In commit 6969515b (KWSys 2013-01-04, 2013-01-04) we brought in KWSys
commit cb5f835f (SystemTools: Fix MakeDirectory with colon in path,
2013-01-02) which removed a useless if condition but did not leave
behind the unconditional resulting behavior.  Add the missing line.
Merge topic 'update-kwsys' into next

64717bb KWSys: Fix SystemTools::MakeDirectory after recent cleanup