Min() seriously broken with 0 (and perhaps max too)

[MartijnR]

see https://docs.google.com/spreadsheets/d/1UQSdqOS1kE8Z3qvMDx9jcnxHOnsJ70xAde7mJksZPtk/edit#gid=0

If any of the non-last fields is 0, the min() function ignores it.

• [x] add tests for min and max where the expcted result is 0 of one of the non-last fields.
• [x] fix it