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