Merge branch 'pw/worktree-list-with-z'

"git worktree list --porcelain" did not c-quote pathnames and lock
reasons with unsafe bytes correctly, which is worked around by
introducing NUL terminated output format with "-z".

* pw/worktree-list-with-z:
  worktree: add -z option for list subcommand

diff --cc Documentation/git-worktree.txt
Simple merge

diff --cc builtin/worktree.c
Simple merge