Posting/Editing: cannot create new post after selecting a hidden site using the site switcher

Steps to reproduce:

1. Open the app.
2. Go to My Sites at the bottom left
3. Choose Switch Site.
4. If you don't already have any hidden sites, tap the more menu at top right and hide one of the sites.
5. Hit the search icon on the top.
6. Tap the text input box and search for a hidden site.
7. Tap a hidden site to choose.
8. See the site is now the current site.
9. Tap new post button at the bottom.

Props @kraftbj for providing the steps to reproduce. 😍

Result: I cannot create a post and two error notices appeared. (29s)

This blog is hidden and couldn't be loaded. Enable it again in settings and try again.

An error occurred when loading the post. Refresh your posts and try again.

^{Tested with WPAndroid alpha-200 on Pixel 3 Android 10.}

Note: when I tested, sometimes I was able to create a new post and sometimes I couldn't. I think this is because sometimes a site visibility change takes place after selecting a hidden site with the site switcher and sometimes it doesn't.

Most of the time, the logs indicate that the site visibility was updated. I spotted one Volley error in one session that seems to be about the post not being able to be created though. I am not sure why it only appeared in some of the sessions, regardless of whether or not the new post button worked.

_{(internal reference: p4k3M4-2BP-p2#comment-2107 cc @kraftbj @maxme)}

Reproduce the failure through My Sites, Switch Site, hidden-site search, and the New Post button on Android. Start by reviewing the site-switcher and post-creation flow alongside the session logs, then verify that selecting a hidden site consistently allows a new post without either error notice.