git-format-patch does not encode lines starting with "From"

Summary
=======

git-format-patch in 2.32.0 fails to quote/escape lines starting with
"From ", and mbox readers conclude there is an empty mail.


Observed
========

$ git commit -m 'subject

From ffffffffffffffffffffffffffffffffffffffff Mon Sep 17 00:00:00 2001
with love.'
$ git format-patch HEAD^!
$ head 0001-subject.patch
From d489071b4855a49b32e9b5ae5addd982d2ed8d7d Mon Sep 17 00:00:00 2001
From: Jan Engelhardt <redacted>
Date: Sun, 27 Jun 2021 20:04:20 +0200
Subject: [PATCH] subject

From ffffffffffffffffffffffffffffffffffffffff Mon Sep 17 00:00:00 2001
with love.

$ git reset --hard HEAD^
$ git am -p0 0001-subject.patch
Patch is empty.
When you have resolved this problem, run "git am --continue".


Expected to see
===============

$ head 0001-subject.patch
From d489071b4855a49b32e9b5ae5addd982d2ed8d7d Mon Sep 17 00:00:00 2001
From: Jan Engelhardt <redacted>
Date: Sun, 27 Jun 2021 20:04:20 +0200
Subject: [PATCH] subject

From ffffffffffffffffffffffffffffffffffffffff Mon Sep 17 00:00:00 2001

with love.

On Sun, Jun 27 2021, Jan Engelhardt wrote:

Summary
=======

git-format-patch in 2.32.0 fails to quote/escape lines starting with
"From ", and mbox readers conclude there is an empty mail.


Observed
========

$ git commit -m 'subject

From ffffffffffffffffffffffffffffffffffffffff Mon Sep 17 00:00:00 2001
with love.'
$ git format-patch HEAD^!
$ head 0001-subject.patch
From d489071b4855a49b32e9b5ae5addd982d2ed8d7d Mon Sep 17 00:00:00 2001
From: Jan Engelhardt <redacted>
Date: Sun, 27 Jun 2021 20:04:20 +0200
Subject: [PATCH] subject

From ffffffffffffffffffffffffffffffffffffffff Mon Sep 17 00:00:00 2001
with love.

$ git reset --hard HEAD^
$ git am -p0 0001-subject.patch
Patch is empty.
When you have resolved this problem, run "git am --continue".


Expected to see
===============

$ head 0001-subject.patch
From d489071b4855a49b32e9b5ae5addd982d2ed8d7d Mon Sep 17 00:00:00 2001
From: Jan Engelhardt <redacted>
Date: Sun, 27 Jun 2021 20:04:20 +0200
Subject: [PATCH] subject

quoted

From ffffffffffffffffffffffffffffffffffffffff Mon Sep 17 00:00:00 2001

with love.

"git format-patch --pretty=mboxrd" and "git am --patch-format" should
solve this issue for you.