Merge branch 'jk/format-patch-number-singleton-patch-with-cover'

"git format-patch --cover-letter HEAD^" to format a single patch
with a separate cover letter now numbers the output as [PATCH 0/1]
and [PATCH 1/1] by default.

* jk/format-patch-number-singleton-patch-with-cover:
format-patch: show 0/1 and 1/1 for singleton patch with cover letter

diff --cc builtin/log.c
Simple merge