build-bash-completion: Check for None before comparing

Comparing a number with None is not a good idea:

  >>> (0 < None, 0 > None)
  (False, True)

This patch also adds build-bash-completion to the list
of checked Python scripts and wraps one line of more
than 80 characters.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>