QTextLayout::draw mishandles clip

1. Create a QTextLayout for a plain text QString consisting of two lines
2. Prepare layout with a loop calling createLine as per QTextLayout documentation
3. call draw() on this layout, giving it a clip parameter that is about one and half lines high

Expected: displayed text is clipped as per clip parameter.  One of the lines is visible, the other is clipped to half-height.

Actual: both lines are visible. Per my reading (and stepping through) the source code, it correctly decides to draw both lines because they both have visible part in the clip area, but skip the actual clipping because there is no selection and excludedRegion remains null.