refs: move the logic to add \t to reflog to the files backend

523fa69c (reflog: cleanse messages in the refs.c layer, 2020-07-10)
centralized reflog normalizaton.  However, the normalizaton added a
leading "\t" to the message. This is an artifact of the reflog
storage format in the files backend, so it should be added there.

Routines that parse back the reflog (such as grab_nth_branch_switch)
expect the "\t" to not be in the message, so without this fix, git
with reftable cannot process the "@{-1}" syntax.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/refs.c b/refs.c
index b1dc816..9d58e17 100644
--- a/refs.c
+++ b/refs.c
@@ -875,7 +875,6 @@
 	char c;
 	int wasspace = 1;
 
-	strbuf_addch(sb, '\t');
 	while ((c = *msg++)) {
 		if (wasspace && isspace(c))
 			continue;
diff --git a/refs/files-backend.c b/refs/files-backend.c
index e0aba23..985631f 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -1628,8 +1628,10 @@
 	int ret = 0;
 
 	strbuf_addf(&sb, "%s %s %s", oid_to_hex(old_oid), oid_to_hex(new_oid), committer);
-	if (msg && *msg)
+	if (msg && *msg) {
+		strbuf_addch(&sb, '\t');
 		strbuf_addstr(&sb, msg);
+	}
 	strbuf_addch(&sb, '\n');
 	if (write_in_full(fd, sb.buf, sb.len) < 0)
 		ret = -1;