Revert "CanvasBase.GradientFill causes a math error"

This reverts commit 1bd4b9091d3649f531c77ef0d0d656de4f6e3129.
Fixes "division by zero" error

eg: Compile DocView and resize the contents panel all the way to the
right. The gradient panel ends up having < 1 width, which means it is
not visible any more, so really the GradientFill doesn't need to do
anything.