fast-import: don't fail on omitted committer name

fast-import format declares 'committer_name SP' to be optional in
'committer_name SP LT email GT'. But for a (commit) object SP is
obligatory while zero length committer_name is ok. git-fsck checks
that SP is present, so fast-import must prepend it if the name SP
part is omitted. It doesn't do so and thus for "LT email GT" ident
it writes a bad object.

Name cannot contain LT or GT, ident always comes after SP in fast-import.
So if ident starts with LT reuse the SP as if a valid 'SP LT email GT'
ident was passed.

This fixes a ident parsing bug for a well-formed fast-import input.
Though the parsing is still loose and can accept a ill-formed input.
Signed-off-by: NDmitry Ivankov <divanorama@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

fast-import.c

@@ -1971,6 +1971,10 @@ static char *parse_ident(const char *buf)
 	size_t name_len;
 	char *ident;
 
+	/* ensure there is a space delimiter even if there is no name */
+	if (*buf == '<')
+		--buf;
+
 	gt = strrchr(buf, '>');
 	if (!gt)
 		die("Missing > in ident string: %s", buf);

t/t9300-fast-import.sh

@@ -352,7 +352,7 @@ data <<COMMIT
 empty commit
 COMMIT
 INPUT_END
-test_expect_failure 'B: accept and fixup committer with no name' '
+test_expect_success 'B: accept and fixup committer with no name' '
 	git fast-import <input &&
 	out=$(git fsck) &&
 	echo "$out" &&