Blender Git Loki

Fix crashes with invisible Outliners on fullscreen or window closing

I didn't actually confirm this is caused by invisible Outliners. But I'm pretty
sure the error happens with Outliners that aren't initialized (so were open in
an area before, but another editor is active there currently).
In that case, the runtime data may not be set yet and that is fine.

Fixes T83420.