isMessageInNarrow: Fix regression in matchRecipients.

[jainkuniya]

Remove normalizedRecipients === ownEmail condition, as it is not
taking narrow in consideration. For self message, display_recipient
will only consist of ownEmail. Thus for calling isMessageInNarrow
with self message and any private narrow was returning true (because
of normalizedRecipients === ownEmail). So remove this condition.

Also improve normalizedNarrow, so that it consist of only unique
values. Now this change will take care of logic which was intended to be
taken by normalizedRecipients === ownEmail (which is getting removed,
by this commit).

Fixes: #3324

[jainkuniya]

@gnprice @borisyankov Let's fix this bug too in the next release.

[gnprice]

Thanks @jainkuniya ! This bug will be good to fix.

I don't love this solution. The existing code is too complicated and lacks conceptual clarity, which is the root cause of the issue -- and the same thing is still true after this change.

One way to see that: what does this matchRecipients function mean? How would you describe it in a jsdoc comment? I think it will be challenging to write a description that is completely accurate and precise and yet is reasonably short, because the function's meaning is somewhat confused. (Which, again, was already true before this change. 🙂 )

Relatedly: a bugfix like this definitely calls for unit tests. 😛 There should be a test added that demonstrates the bug, and would fail on the old code.

[gnprice]

(Let's continue on the issue thread.)