Random maximum values on Histogram

[gselzer]

Currently easiest to see on pygfx, where the only vertical axis tick is the maximum bin count:

Repeated by running examples/numpy_arr.py with ndv.data.cells3d and clicking on the histogram button for the (only) channel.

Haven't dug too much into it yet - seems like the wrong slice is being passed through to array_canvas.py::_calc_hist_bins, but that doesn't make much sense at all as that data also goes to the image handle...