Regression: Path filling performance improvement can cause infinite loop

Commit 6506e0a6eec67985432427c630b148e825184c5d / http://codereview.qt-project.org/#change,11007 improved path filling performance with the raster paint engine. Unfortunately the fix caused a regression in WebKit's fast/canvas/canvas-largedraws.html layout test, causing QBezier::addToPolygon to enter an infinite loop adding points to the polygon endlessly.

The attached test case provides the same input values used by the layout test in a standalone .cpp using QPainterPath/QPainter/QImage - it reproduces the hang for me.