Correct handling of font weights bolder than bold.

A couple of places were checking for a font weight equal to QFont::Bold
rather than a weight that is greater or equal to this. This sometimes
results in QFont::Black being rendered with a lighter weight than
QFont::Bold even though it should if anything be heavier.

Change-Id: I5aa73a84ea2718783bbac93a031d87b2ad90012c
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>