Error when saving a scene using native file dialog

[timothyqiu]

Tested versions

master[4a01602]

System information

Arch Linux

Issue description

When "Use Native File Dialogs" is enabled, saving a scene produces these errors:

ERROR: Do not use progress dialog (task) while flushing the message queue or using call_deferred()!
   at: add_task (editor/progress_dialog.cpp:155)
ERROR: Condition "!tasks.has(p_task)" is true. Returning: canceled
   at: task_step (editor/progress_dialog.cpp:188)
ERROR: Condition "!tasks.has(p_task)" is true. Returning: canceled
   at: task_step (editor/progress_dialog.cpp:188)
ERROR: Condition "!tasks.has(p_task)" is true. Returning: canceled
   at: task_step (editor/progress_dialog.cpp:188)
ERROR: Condition "!tasks.has(p_task)" is true. Returning: canceled
   at: task_step (editor/progress_dialog.cpp:188)
ERROR: Condition "!tasks.has(p_task)" is true. Returning: canceled
   at: task_step (editor/progress_dialog.cpp:188)
ERROR: Condition "!tasks.has(p_task)" is true.
   at: end_task (editor/progress_dialog.cpp:215)

The scene is saved nevertheless.

Steps to reproduce

1. Turn on interface/editor/use_native_file_dialogs in editor settings.
2. Create a new scene.
3. Save the scene.

Minimal reproduction project (MRP)

N/A

[bruvzg]

I can't reproduce it on macOS, probably related to the fact native file dialog are non-blocking on Linux (API limitation) or it's caused by call_deferred (Linux native dialogs are handled from the thread).

The core of the issues is likely EditorProgressDialog and the way long tasks in the editor are handled (blocking main thread and trying to run main event loop iterations manually in the process).