Disallow merged cells in Excel input for fmudesign

[tommyod]

Closes #667

[berland]

What happens for users with xls files that have accicentally(?) merged some cells and using those xls files in their FMU setups? Could there be a situation where the merged cells are not involved in the operations and thus it would work fine, but break now?

[berland]

From a Kusto query, there seems to be a few users running fmudesign as a workflow in Ert. I extracted xlsx filenames (31 unique the last 6 months) and ran the new fmudesign on these. I got no errors about merged cells so this is probably safe to merge.

(additionally I could see from the logs that they did not necessarily use the Komodo fmudesign so they don't even get the benefit)

[tommyod]

What happens for users with xls files that have accicentally(?) merged some cells and using those xls files in their FMU setups? Could there be a situation where the merged cells are not involved in the operations and thus it would work fine, but break now?

It would fail. Yes, that is possible. As such it is a breaking change, but not a breaking change wrt expected, correct input. So I would consider it a bugfix.

Good that you did a check!