ValueError when cutting out Auckland domain

### Describe the bug

Doing a cutout of the Auckland domain gives the following error from iris's `cube.intersection`.

> ValueError: coordinate units with no modulus are not yet supported

I'd hazard that this is due to the domain crossing the date line.

### How to reproduce
Steps to reproduce the behaviour:

1.
2.
3.

### Expected behaviour

### Environment

- Version: [e.g. from `cset --version`]
- Browser (if UI issue): [e.g. Chrome, Firefox]

Start by reproducing an Auckland-domain cutout and trace the call into iris's cube.intersection, focusing on the reported coordinate-units-with-no-modulus error and possible date-line crossing. Done means the Auckland cutout completes without this ValueError.

Written by the indexing model from the issue text.