subscriptions: Fix buggy behaviour of click event handlers.
subscriptions: Fix buggy behaviour of click event handlers.

This commit fixes a bug where clicking on a stream row on the left
in the subscriptions table called the ".stream-row" as well as the
".sub_unsub_button" click events in `stream_edit.js`.

This caused the stream subscription to toggle everytime the row was
clicked. Also, this bug is only observed if the ".sub_unsub_button"
had been clicked first.

eeshangarg/zulip,punchagan/zulip,hackerkid/zulip,kou/zulip,kou/zulip,andersk/zulip,brainwane/zulip,brainwane/zulip,eeshangarg/zulip,punchagan/zulip,rht/zulip,rht/zulip,andersk/zulip,hackerkid/zulip,andersk/zulip,kou/zulip,punchagan/zulip,zulip/zulip,andersk/zulip,kou/zulip,punchagan/zulip,hackerkid/zulip,showell/zulip,punchagan/zulip,kou/zulip,rht/zulip,zulip/zulip,showell/zulip,showell/zulip,rht/zulip,eeshangarg/zulip,rht/zulip,andersk/zulip,showell/zulip,zulip/zulip,eeshangarg/zulip,rht/zulip,punchagan/zulip,hackerkid/zulip,brainwane/zulip,eeshangarg/zulip,brainwane/zulip,zulip/zulip,kou/zulip,andersk/zulip,showell/zulip,brainwane/zulip,hackerkid/zulip,zulip/zulip,kou/zulip,hackerkid/zulip,punchagan/zulip,rht/zulip,brainwane/zulip,eeshangarg/zulip,eeshangarg/zulip,showell/zulip,andersk/zulip,zulip/zulip,showell/zulip,hackerkid/zulip,brainwane/zulip,zulip/zulip