Merge branch 'jk/add-p-unmerged-fix'

"git add -p" while the index is unmerged sometimes failed to parse
the diff output it internally produces and died, which has been
corrected.

* jk/add-p-unmerged-fix:
  add-patch: handle "* Unmerged path" lines

diff --cc add-patch.c
Simple merge

diff --cc t/t3701-add-interactive.sh
Simple merge