[BUG] git send-email: incorrectly parses email address with comma

Git send-email allows to combine multiple email addresses in one
parameter, e.g.

--to="a@example.com, b@example.com"

But email addresses may contain commas themselves:

--to="LASTNAME, firstname [off-list ref]"

This may lead to an error:
$ git send-email --to="Schuchardt, Heinrich [off-list ref]" \
0000*.patch0000-cover-letter.patch
(mbox) Adding cc: Heinrich Schuchardt [off-list ref] from
line 'From: Heinrich Schuchardt [off-list ref]'

From: Heinrich Schuchardt <redacted>
To: Schuchardt,
        Heinrich [off-list ref]
Subject: [PATCH 0/2] efi_loader: adjust definitions of variable services
Date: Sat, 12 May 2018 10:01:21 +0200
Message-Id: [off-list ref]
X-Mailer: git-send-email 2.17.0

Send this email? ([y]es|[n]o|[q]uit|[a]ll): a
Password for 'smtp://xypron.glpk@example.com@mail.example.com:587':
Syntax error in parameters or arguments



Please, implement the following logic,

If the string preceding a comma is not a valid email address do not
split it off.

Best regards

Heinrich Schuchardt