We consistently either pass a `then_select_id` into narrow.activate,
or were using the select_first_unread option. Now, we just compute
select_first_unread based on the value of then_select_id.
Apparently, we were incorrectly passing through something related to
opts.use_initial_narrow_pointer as the value for `use_first_anchor`.
If you read the logic in narrow.js carefully,
use_initial_narrow_pointer was unconditionally false.
The correct value for this attribute is when we're trying to narrow to
the first unread message in a given context. There are two things to
check:
* then_select_id is -1; i.e. we don't have a specific message ID we're
trying to narrow around.
* select_first_unread is True, i.e. we're trying to narrow to the
first unread message.
A bit more work should allow us to get rid of the second condition,
but I'm not quite confident enough to do that yet.
Tim Abbott
Steve Howell