New post: setting status to Published then tapping on "Save as draft" doesn't work

[mzorz]

Expected behavior

If the Post hasn't been published yet, both editing the status through Post Settings and saving or by tapping Save as draft on the overflow menu should have the same results.

Actual behavior

Once the status of a new post has been changed to Published through Settings, the Save as draft option doesn't work. You can make it work again by changing the status to Draft back manually.

Steps to reproduce the behavior

1. start a new draft
2. enter something in title and body
3. tap on the menu icon and tap on Settings
4. change the post status from Draft to Published
5. go back to editing
6. now open the overflow menu again
7. tape Save as draft
8. observe a snackbar is shown "Your post is uploading" but nothing really happens (nothing is being sent to the server - no upload notification is shown).

Tested on [Pixel 2], Android [8.1], WPAndroid [develop]

[mzorz]

Closing via #9661