Aviation Colour State failures

[daflack]

Describe the bug

The aviation colour state fails when multiple models are used but only one orography field is given.

How to reproduce

Steps to reproduce the behaviour:

1. Enter two models into the workflow gui.
2. Select Aviation colour state/Aviation colour state due to cloud base.
3. See that it fails.

Expected behaviour

Aviation colour state should calculate based on the orography field provided, but if only one is given the assumptions around sea level should be printed as warnings.