Publisher: Fix stop of publishing

[iLLiCiTiT]

Changelog Description

Fixed issues related to stopped/paused publishing.

Additional info

The issue was introduced with #689 . When publishing was paused it could happen that the publishing loop was added to main process items more than once, in that case there were 2 running loops of plugin processing, leading to triggering the process loops more than once at the end.

Traceback

Traceback (most recent call last):
  File "../ayon-core/client/ayon_core/tools/publisher/control_qt.py", line 52, in _execute
    item.process()
  File "../ayon-core/client/ayon_core/tools/publisher/control_qt.py", line 20, in process
    self.callback(*self.args, **self.kwargs)
  File "../ayon-core/client/ayon_core/tools/publisher/control_qt.py", line 95, in _next_publish_item_process
    func = self._publish_model.get_next_process_func()
  File "../ayon-core/client/ayon_core/tools/publisher/models/publish.py", line 918, in get_next_process_func
    item = next(self._main_thread_iter)
StopIteration

Testing notes:

I could not replicate the issue in traypublisher, so it requires to test in DCCs (could be replicated in nuke, maya, houdini).

1. Open DCC of your choice.
2. Open publisher.
3. Start publishing with validate button, or start publishing and stop it via Stop button.
4. Continue publishing with Publish button.
5. Check output (in script editor or console, based on DCC).
6. There should not be traceback similar to traceback above.

[BigRoy]

The issue of this error:

Traceback (most recent call last):
  File "E:\dev\ayon-core\client\ayon_core\tools\publisher\control_qt.py", line 52, in _execute
    item.process()
  File "E:\dev\ayon-core\client\ayon_core\tools\publisher\control_qt.py", line 20, in process
    self.callback(*self.args, **self.kwargs)
  File "E:\dev\ayon-core\client\ayon_core\tools\publisher\control_qt.py", line 95, in _next_publish_item_process
    func = self._publish_model.get_next_process_func()
  File "E:\dev\ayon-core\client\ayon_core\tools\publisher\models\publish.py", line 930, in get_next_process_func
    item = next(self._main_thread_iter)
StopIteration

Upon validate, and then after continuing the publish is gone. I was unable to reproduce that error so this seems to be completely functional and fix the issue.

I tested in Maya 2024, Blender 4.2, Houdini 20.0.724 and Fusion 18. All good.
Resetting publisher, and republishing also seems to work.

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I did a quick read over the code but it was a bit hard to grasp how and why this fixes it - so I couldn't say much about that. Sorry! ⚠️