Crashes with complex autoindent

[aycabta]

Reported by @mame:

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Reported at #16453 by @JunichiIto

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[BenKanouse]

I attempted to fix this issue here: #56

Please let me know if you have any feedback.

Thanks!

[BenKanouse]

I believe that this PR fixes both issues: #58

It also adds test for both issues. I'm looking forward to any feedback. Thanks!