config: avoid segfault when parsing command-line config

We already check for an empty key on the left side of an
equals, but we would segfault if there was no content at
all.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -46,6 +46,8 @@ static int git_config_parse_parameter(const char *text,
 	struct strbuf **pair;
 	strbuf_addstr(&tmp, text);
 	pair = strbuf_split_max(&tmp, '=', 2);
+	if (!pair[0])
+		return error("bogus config parameter: %s", text);
 	if (pair[0]->len && pair[0]->buf[pair[0]->len - 1] == '=')
 		strbuf_setlen(pair[0], pair[0]->len - 1);
 	strbuf_trim(pair[0]);

t/t1300-repo-config.sh

@@ -918,4 +918,8 @@ test_expect_success 'git -c complains about empty key' '
 	test_must_fail git -c "=foo" rev-parse
 '
 
+test_expect_success 'git -c complains about empty key and value' '
+	test_must_fail git -c "" rev-parse
+'
+
 test_done