Here is a scenario that could happen before this commit:
1. go to a list view with more than one record, say 3
2. click on the 3rd record to open the form view
3. the pager says 3/3
4. click on edit button
5. click on discard button
6. the pager says 1/3 (but the record displayed is still the same)
It is often necessary to restore the offset for the sub records, because
the number of pages in a one2many could have changed. However, it is
not a good idea to do that for the main record, since it interferes with
the usual flow of operations.