Radial distribution errors over occasional cells

I've noticed the radial distribution is occasionally not calculated correctly, especially when the cell is approaching vertical orientation. This is most evident when trying to reconstruct the image. Tracked down to a single bug, have a look at the PR.

To reproduce, initialise over the bitmap and parameters provided in #119 and reconstruct over the binary channel. (The issue is the same with fluorescence channels, not shown here for sake of brevity) - this is what I get, which is not correct.