Axonometric grid unusable when spacing set to larger values

[Rad3k]

Steps to reproduce:

1. Open new document (default size, A4)
2. Create new axonometric grid with e.g. 16px spacing.
3. Set zoom to 100%. You should notice that almost no gridlines are drawn.
4. If you try to zoom in, some will pop up, but regardless of zoom you'll be seeing no more than few gridlines in whole window.

It seems like the minimal grid spacing when scaled (or maximal displayed grid density) somehow depends on the actual grid spacing (set in document settings) - the larger the grid, the fewer gridlines are visible, regardless of zoom.

I've looked into the code and managed to fix that. It's still somewhat messy, but at least it works properly.
I'm attaching a patch, feel free to apply it to the development tree (if someone else hadn't fixed it yet).

[Rad3k (trueradzian)]

Attaching a patch ported to 0.47

[Johan Engelen (johanengelen)]

I'm sorry I did not notice your patch earlier. Great work! Committed in r9331