Release post lock when switching user from the post editing screen

[johnbillion]

A slightly annoying behaviour is that when switching users from the post editing screen, the post lock isn't released and you see the "This post is being edited by X" modal, and you need to take over.

User Switching should release the post lock when switching between users from this screen.

Steps to reproduce:

• Switch to a user
• Edit a post
• Use the "Switch back" option in the user profile menu
• See the post locked modal