Rose edit sometimes eats rows in tables

[jfrost-mo]

When you have a repeating set of compound fields for a config setting, it relies on other unrelated compound fields having a value, otherwise it will not save the value.

This occurs on setups that have this kind of metadata setup:
https://github.com/MetOffice/CSET/blob/638f0185de052b83e207d96436bff00aa0d37c75/cset-workflow/meta/diagnostics/rose-meta.conf#L8-L23

Here is a video demonstrating the issue:

eating_rows.mp4

I think it is causes by compound fields that are currently empty, so there is no value in the rose-suite.conf file for them.

This issue also ails rose 2019.