compose: Fix bug where stream color didn't update on mouse selection.
compose: Fix bug where stream color didn't update on mouse selection.

Called the `decorate` function to update stream color in the compose
box on `change` instead of `blur`.

On clicking on a stream option, the input box for the stream name
remained in focus, hence decorate wasn't triggered on blur. Using
the change event instead, ensures that decorate will be called
anytime the stream is changed.

Fixes: #20871

rht/zulip,zulip/zulip,zulip/zulip,rht/zulip,kou/zulip,kou/zulip,zulip/zulip,zulip/zulip,kou/zulip,andersk/zulip,rht/zulip,rht/zulip,kou/zulip,andersk/zulip,rht/zulip,rht/zulip,zulip/zulip,rht/zulip,kou/zulip,kou/zulip,andersk/zulip,andersk/zulip,zulip/zulip,kou/zulip,andersk/zulip,andersk/zulip,andersk/zulip,zulip/zulip