Identify what can lead to invalid parent task indentation

[opatry]

It's possible to generate a case where the indentation of a parent task is not 0 which should be the case.
Determine which conditions can lead to that.

Tip

Idea for now: moving a child task from one list to another

See:

• Crash loop when invalid indentation is detected #265
• Workaround invalid parent task indentation to avoid crash loop at app start #266

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• Evaluate if Improve logging mechanism #118 couldn't be handled at the same time to better this kind of issue in the future:
  • log user actions
  • log non fatal error when requirements like that are not meant and recover from it
• Evaluate if sanity check couldn't be made at start with auto fix when possible (like Google Tasks does sanity checks on broken list indentation, would be nice to replicate #151 ?)