The issue was caused by Cycles display driver not being able to restore
window's OpenGL context after disposing Cycles-side OpenGL context.
This is due to the window OpenGL re-activation needing to access window
manager which gets cleared out form global main during file reading.
Defer clearing window manager from the global main to until after all
screens are "exited". This allows Cycles to properly stop rendering,
dispose its OpenGL context, and restore window's drawable context.
It is unclear why it was required to clear window manager list early
on. Guess is that it comes from an original code in a1c8543f2a where
there was an early return which then got replaced with an actual logic
without changing the order of de-initialization and window manager list
clear.
Differential Revision: https://developer.blender.org/D13799
7a2b181591