CancelAllDialogs action doesn't work

[luhan2017]

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Version

latest master

Describe the bug

CancelAllDialogs action doesn't work as expected.

To Reproduce

Steps to reproduce the behavior:

1. Go to Microsoft.Bot.Builder.TestBot.Json
2. Start the bot
3. Run sample 13. EndDialog
4. See screenshot, call CancelAllDialogs will throw an exception.

The dc.Parent.CancelAllDialogsAsync is not executed.

Expected behavior

Give a clear and concise description of what you expected to happen.

Screenshots

If applicable, add screenshots to help explain your problem.

Additional context

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[bug]

[vishwacsena]

Fixed via #3536