nmbug backtrace due to .mailmap

[Jani Nikula]

Presumably because of the .mailmap added in nmbug repository:

commit 5ea99ebcb7d188003bf4854b566f6d21721f5ea1
Author: W. Trevor King <wking at tremily.us>
Date:   Mon Oct 16 10:46:27 2017 -0700

    .mailmap: Consolidate David and Tomi's author names
    
    The format is documented in git-shortlog(1).  In both cases, I've
    prefered the email used for their most-recent commit.

A       .mailmap

I now get backtrace trying to nmbug pull:

Traceback (most recent call last):
  File "/home/jani/bin/nmbug", line 834, in <module>
    args.func(**kwargs)
  File "/home/jani/bin/nmbug", line 433, in pull
    _insist_committed()
  File "/home/jani/bin/nmbug", line 412, in _insist_committed
    status = get_status()
  File "/home/jani/bin/nmbug", line 580, in get_status
    maybe_deleted = _diff_index(index=index, filter='D')
  File "/home/jani/bin/nmbug", line 658, in _diff_index
    for id, tag in _unpack_diff_lines(stream=p.stdout):
  File "/home/jani/bin/nmbug", line 678, in _unpack_diff_lines
    'Invalid line in diff: {!r}'.format(line.strip()))
ValueError: Invalid line in diff: u'.mailmap'

I also didn't see any discussion about adding a .mailmap prior to it
being pushed.


BR,
Jani.