Avoid saving scene while already saving the scene

[KoBeWi]

Fixes #85093
Does not fix my crash unfortunately.

[YuriSizov]

I wasn't sure about a solution like this. I think that this will prevent the updated script from saving. We first save the scene then the script editor modifies the script to add an empty new line, and then we attempt to save the same scene again, but this won't happen as far as I can tell.

In a pinch this is not the worst thing, but we need to handle this somehow, ideally.

[KoBeWi]

There are multiple callbacks for applying some changes before saving, like NOTIFICATION_EDITOR_PRE_SAVE or apply_changes(). ScriptEditor should use that instead of modifying the script while it's being saved.

[akien-mga]

There are multiple callbacks for applying some changes before saving, like NOTIFICATION_EDITOR_PRE_SAVE or apply_changes(). ScriptEditor should use that instead of modifying the script while it's being saved.

Do you want to try that approach? 👀

[KoBeWi]

I was thinking that it can be done independently (tbh the case prevented in this PR might even deserve an error message), but I could do it in this PR.

[akien-mga]

Discussed with Yuri, should be a good approach for now to prevent the crash.

[akien-mga]

Thanks!