Merge branch 'lt/diff-stat-show-0-lines' into maint

"git diff --stat" miscounted the total number of changed lines when
binary files were involved and hidden beyond --stat-count.  It also
miscounted the total number of changed files when there were
unmerged paths.

* lt/diff-stat-show-0-lines:
  t4049: refocus tests
  diff --shortstat: do not count "unmerged" entries
  diff --stat: do not count "unmerged" entries
  diff --stat: move the "total count" logic to the last loop
  diff --stat: use "file" temporary variable to refer to data->files[i]
  diff --stat: status of unmodified pair in diff-q is not zero
  test: add failing tests for "diff --stat" to t4049
  Fix "git diff --stat" for interesting - but empty - file changes