Fix bug with (un)subscribe button showing on wrong narrow.
Fix bug with (un)subscribe button showing on wrong narrow.

We had a bug for a while where if somebody subscribed you to a
stream, and you were narrowed to another stream, we'd show
a button in the "trailing bookend" to "Unsubscribe" from the
current stream.  I'm not sure how long we had that bug, but it
was at least a couple months old, and I couldn't track down an
issue for it.

Now we make sure that the stream event for the subscription is
related to the current narrow.

Users should still see messages when they subscribe/unsubscribe
themselves or when another user re-subscribes them to the stream
that they are narrowed to.

vaidap/zulip,jphilipsen05/zulip,jphilipsen05/zulip,dhcrzf/zulip,verma-varsha/zulip,SmartPeople/zulip,tommyip/zulip,jackrzhang/zulip,SmartPeople/zulip,christi3k/zulip,verma-varsha/zulip,zulip/zulip,synicalsyntax/zulip,christi3k/zulip,kou/zulip,Galexrt/zulip,tommyip/zulip,jackrzhang/zulip,rishig/zulip,Galexrt/zulip,showell/zulip,vaidap/zulip,showell/zulip,jackrzhang/zulip,kou/zulip,amanharitsh123/zulip,timabbott/zulip,vabs22/zulip,timabbott/zulip,rht/zulip,dhcrzf/zulip,vabs22/zulip,brockwhittaker/zulip,andersk/zulip,brainwane/zulip,kou/zulip,dhcrzf/zulip,kou/zulip,showell/zulip,eeshangarg/zulip,Galexrt/zulip,j831/zulip,amanharitsh123/zulip,jphilipsen05/zulip,jackrzhang/zulip,synicalsyntax/zulip,brockwhittaker/zulip,dhcrzf/zulip,Galexrt/zulip,tommyip/zulip,ryanbackman/zulip,christi3k/zulip,christi3k/zulip,showell/zulip,punchagan/zulip,brockwhittaker/zulip,showell/zulip,rishig/zulip,rht/zulip,timabbott/zulip,jphilipsen05/zulip,jackrzhang/zulip,jrowan/zulip,timabbott/zulip,kou/zulip,showell/zulip,hackerkid/zulip,rht/zulip,jrowan/zulip,Galexrt/zulip,punchagan/zulip,shubhamdhama/zulip,amanharitsh123/zulip,andersk/zulip,jrowan/zulip,hackerkid/zulip,shubhamdhama/zulip,verma-varsha/zulip,zulip/zulip,verma-varsha/zulip,brockwhittaker/zulip,rishig/zulip,dhcrzf/zulip,synicalsyntax/zulip,j831/zulip,mahim97/zulip,andersk/zulip,SmartPeople/zulip,rishig/zulip,vaidap/zulip,rht/zulip,vaidap/zulip,jphilipsen05/zulip,brockwhittaker/zulip,andersk/zulip,andersk/zulip,eeshangarg/zulip,eeshangarg/zulip,shubhamdhama/zulip,vabs22/zulip,j831/zulip,SmartPeople/zulip,rht/zulip,hackerkid/zulip,brainwane/zulip,christi3k/zulip,ryanbackman/zulip,timabbott/zulip,brainwane/zulip,dhcrzf/zulip,mahim97/zulip,zulip/zulip,rht/zulip,punchagan/zulip,synicalsyntax/zulip,vaidap/zulip,eeshangarg/zulip,zulip/zulip,synicalsyntax/zulip,rht/zulip,kou/zulip,timabbott/zulip,brockwhittaker/zulip,andersk/zulip,hackerkid/zulip,hackerkid/zulip,zulip/zulip,tommyip/zulip,jackrzhang/zulip,shubhamdhama/zulip,j831/zulip,jrowan/zulip,christi3k/zulip,tommyip/zulip,punchagan/zulip,ryanbackman/zulip,brainwane/zulip,tommyip/zulip,amanharitsh123/zulip,vabs22/zulip,andersk/zulip,jrowan/zulip,eeshangarg/zulip,kou/zulip,brainwane/zulip,mahim97/zulip,jrowan/zulip,amanharitsh123/zulip,vabs22/zulip,amanharitsh123/zulip,ryanbackman/zulip,mahim97/zulip,hackerkid/zulip,mahim97/zulip,mahim97/zulip,shubhamdhama/zulip,j831/zulip,vabs22/zulip,SmartPeople/zulip,rishig/zulip,punchagan/zulip,brainwane/zulip,dhcrzf/zulip,zulip/zulip,showell/zulip,ryanbackman/zulip,verma-varsha/zulip,jackrzhang/zulip,rishig/zulip,shubhamdhama/zulip,eeshangarg/zulip,synicalsyntax/zulip,punchagan/zulip,SmartPeople/zulip,Galexrt/zulip,jphilipsen05/zulip,synicalsyntax/zulip,vaidap/zulip,brainwane/zulip,ryanbackman/zulip,eeshangarg/zulip,verma-varsha/zulip,Galexrt/zulip,zulip/zulip,shubhamdhama/zulip,hackerkid/zulip,timabbott/zulip,tommyip/zulip,rishig/zulip,punchagan/zulip,j831/zulip