Fix a bug: cancel of configure cmd cause empty yml

Thank you for excellent software.
When I tested, I encountered lost of yaml config data.
I try to fix it.
I am glad if this patch is useful.

Best regards,
  yoyama

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If configure command is caneled by ctrl-c,
all data in .bakthat.yml are lost.
Only empty file exists.

Re-produce:
  1. >bakthat configure
  2. Ctrl-C