Let's assume the following situation:
- an empty editable x2many list with date field (or any other
fixed width field) and optional fields
- add a record to the list, but discard it directly
- toggle an optional field
After those steps, the date field doesn't have its hardcoded,
absolute width anymore.
This rev. fixes this issue by clarifying the way the stored widths
are erased when the columns change, preventing to reach a corner
case in which we have stored widths, but we can't apply them, and
thus let the browser uniformly divide the space amongst columns.
Aaron Bohy
85bfef9ced