fix #10894: input window start = min, end = max

Investigating https://trac.openmicroscopy.org.uk/ome/ticket/10894 revealed a probable mix-up in `StatsFactory`: the other code in `StatsFactory` and `RenderingSettingsImpl` seems to assume that the input window has a start smaller than its end. In reviewing this PR, make sure that the change seems consistent with the related code and that it doesn't newly break anything in the renderer. (@joshmoore and @jburel can probably answer questions about the code.)