Error resolve for tie game of Tic-Tac-Toe

[Rozaki0318]

I have been enjoying your Tic-Tac-Toe Game and found a following error.

Then, I have added lines to return move = 0 to comMove() function.

I am looking forward to merging this change.

Thanks,

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$ python3 TicTacToe.py 
Do you want to play a game (Y/N): Y
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Welcome to the tic tac toe game

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...

Enter a position between 1 to 9: 4
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 X | O | X
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 X | X | O
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 O | X | O
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Traceback (most recent call last):
  File "TicTacToe.py", line 136, in <module>
    main()
  File "TicTacToe.py", line 119, in main
    insertLetter("O", move)
  File "TicTacToe.py", line 4, in insertLetter
    board[pos] = letter
TypeError: list indices must be integers or slices, not NoneType