Hiding a composer should explicitly save a draft

[julianlam]

When a composer is opened (either by attempting to create a new topic/post, or by editing an existing post), and immediately hidden, the composer disappears and it is not immediately apparent what happened to it.

Was it merely hidden, or actually discarded?

For better UX, either explicitly save a draft (even if nothing was changed), or throw an alert notifying the user that the draft was discarded as there was no content/changes.