I can't have a look at the moment but blindly I remember that in this method there are probably #defines for different platforms. So are you sure it's really unused?
Yes it is (unused).
It is set to true if there is rect-data or normal text, but never used later in the function.
The only distinction is done between rect-data and normal data.
It first appeared in the scintilla 3.5.0-branch in svn r9893 ("* prepare branch for merge to trunk") .