git-am drops colons in the beginning of a subject line

Hey there,

git-am seems to omit colons in the beginning of a subject line.

I have the following simple patch (just an example):

    $ cat 0001-four-colons-prepended.patch
    From e8213a2d10a61c9dc75521d88d656b8d5330e6bb Mon Sep 17 00:00:00 2001
    From: Max Filenko <contact@filenko.ms>
    Date: Tue, 12 Feb 2019 12:21:21 +0100
    Subject: [PATCH] :::: four colons prepended
    
    ---
     file.txt | 2 +-
     1 file changed, 1 insertion(+), 1 deletion(-)
    
    diff --git a/file.txt b/file.txt
    index 4dd1ef7..b5da95d 100644
    --- a/file.txt
    +++ b/file.txt
    @@ -1 +1 @@
    -This is a file.
    +This is a plain text file.
    -- 
    2.17.2 (Apple Git-113)

I apply this patch:

    $ git am 0001-four-colons-prepended.patch
    Applying: four colons prepended

As you might have already noticed git message above doesn't have colons.

Let's double check this:

    $ git show
    commit 6341a6a2872f850ecb376c268b1b3bae54a6a74f (HEAD -> master)
    Author: Max Filenko <contact@filenko.ms>
    Date:   Tue Feb 12 12:21:21 2019 +0100
    
        four colons prepended
    
    diff --git a/file.txt b/file.txt
    index 4dd1ef7..b5da95d 100644
    --- a/file.txt
    +++ b/file.txt
    @@ -1 +1 @@
    -This is a file.
    +This is a plain text file.

The commit message reads 'four colons prepended' while it should read ':::: four colons prepended'.

Colons are missing in the commit message after apllying this patch.

I don't think that's an expected behaviour, isn't it?

-- Cheers, Max