Fixes Scene corruption when child scene is renamed in another directory

[OXTyler]

Fixes #80379
The issue was that _save_scenes_after_move(..) is used both before, and after updating the file, so on the second save it tries to access a file that no longer exists, because it was renamed.

[KoBeWi]

This fixes the rename issue, but it's still possible to break the scene by moving the file.

Also these errors are still printed (not really related though):

  C:\godot_source\editor/progress_dialog.cpp:156 - Do not use progress dialog (task) while flushing the message queue or using call_deferred()!
  C:\godot_source\editor/progress_dialog.cpp:189 - Condition "!tasks.has(p_task)" is true. Returning: canceled
  C:\godot_source\editor/progress_dialog.cpp:189 - Condition "!tasks.has(p_task)" is true. Returning: canceled
  C:\godot_source\editor/progress_dialog.cpp:216 - Condition "!tasks.has(p_task)" is true.

[akien-mga]

Thanks!

[Deozaan]

Please forgive my ignorance. I'm unfamiliar with the usual bugfix/patching process/timeline. I understand that this has been merged into master and will be in 4.2 which should release in November. But what's the likelihood of this being cherrypicked/backported to 4.1.x, and the ETA for that if it will happen?

I lost some work and plenty of time trying to figure out what went wrong and recover the lost work a few days ago due to the issue this fixes. Or maybe it was the issue fixed by #81657? I'm not really sure.

What I know is that I created an MRP in 4.1.1 that I can reliably reproduce editor crashing and scene corruption in, then came to report the bug but found that it's fixed in 4.2-dev5 already. In short: I'm eager to have the fix so the scene corruption doesn't happen again. 🙂

[YuriSizov]

@Deozaan Neither PR is currently expected to make its way into 4.1.x. Not sure about this one, but the other change is potentially dangerous and needs to be proven with time. We don't want a regression to make things even worse in a patch release.

[Deozaan]

Understood. Thank you.