Area field in Land Use table is NULL when a land use layer is created.

[gregmaya]

However, when you update the feature's land use category, it does update the value.

[jorgegil]

I've fixed the calculation of land use area and frontage length when features are added. Sometimes it would have the wrong value, not NULL.

It's important because when adding a feature the category is usually set and correct, and we don't want to update it again.