[FIX] web: keep pager in popup list view

When an action opens records in list (or other) mode in a popup (target:new), the pager should be kept. It can be removed in form view.
Fixes #742
[FIX] mail: partners with missing/invalid emails must not halt notifications to others
[FIX] web_kanban: wrong condition to reset the dataset index

This is related to rev. a218a9ed3f6c965820f2ebdf76ee0e6c89c59a0c

The condition is good, but not in the right place: It should be done once all read_slice (all columns records) are fetched, not at each read_slice end