Don't edit current when changing docks v2

[kitbdev]

• redo of Don't edit current when changing docks (reverted) #90816
• fixes Toggling distraction-free mode selects (or opens) a fixed script in the script list #90654

Made the edit(nullptr) in NOTIFICATION_PREDELETE not run when exiting, since it doesn't need to clean up anything if exiting.
The object was apparently freed but not null, causing a crash on some platforms.

Needs testing on Linux and macOS to make sure #90816 (comment) doesn't happen.

Edit: made sure it works when there is no EditorNode, like in dotnet glue binding.

[KoBeWi]

This is basically same as #90816, but with a safeguard against exit crash.

[akien-mga]

Seems to work fine on Linux.

[akien-mga]

Thanks!