Off-by-one error in QScrollArea::ensureWidgetVisible

After launching the test program (main.cpp), press B. Notice that there is no 1-pixel gap below the blue rectangle even through I asked for a 1-pixel margin (bottom.png). Now press T. Notice that there is now a 1-pixel gap above the red rectangle (top.png).

I'm fairly sure (though not certain) that fixing this bug involves inserting + 1 on this line and this line.

The bug is probably due to this:

QRect rect;
rect.bottomRight() - rect.topLeft() != QPoint{rect.width(), rect.height()};

...which has been the cause of numerous bugs in my own code.