message-fetch: Update empty narrow check to include opts message list.
message-fetch: Update empty narrow check to include opts message list.

In 16c45aa, the check for an empty narrow was updated to no longer
confirm if no messages were returned by the message fetch request.

Updates the empty narrow check to confirm that the messages fetched,
and being processed are for the current / narrow message list before
showing an empty narrow.

zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip