Waypoint splitting in PolarRoute goes one split depth too deep

[hjabbot]

The _split_loc method appears to be going too deep when trying to perform waypoint splitting in PolarRoute. The issue exists in environment_mesh.py hence the issue is being raised here.

The line if (cb_width < min_dcx) or (cb_height < min_dcy): should be changed to if (cb_width <= min_dcx) or (cb_height <= min_dcy): since the cb_width should equal min_dcx at max split depth.

I have done a quick test and can confirm that this prevents the waypoint splitting going too far. I have not done much more than that though, so some more rigorous testing should be done with this change in order. I have created a new branch with this change called split_loc_hotfix