Image Viewer Example - Fit to Window resize doesn't always repaint correctly

Running the Qt 5 Image Viewer example exhibits a problem when fit to window is enabled. If you open an image and resize the window small and then gradually larger, the window doesn't always repaint correctly. This is a regression from Qt 4.8.

Tested with qtbase 34cd8fd566cd61385db12112d9515b0d5388dad3.