am: fix incorrect exit status on am fail to abort

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/am.c

@@ -2106,7 +2106,8 @@ static void am_abort(struct am_state *state)
 	if (!has_orig_head)
 		oidcpy(&orig_head, the_hash_algo->empty_tree);
 
-	clean_index(&curr_head, &orig_head);
+	if (clean_index(&curr_head, &orig_head))
+		die(_("failed to clean index"));
 
 	if (has_orig_head)
 		update_ref("am --abort", "HEAD", &orig_head,

t/t4151-am-abort.sh

@@ -197,7 +197,7 @@ test_expect_success 'am --abort leaves index stat info alone' '
 	git diff-files --exit-code --quiet
 '
 
-test_expect_failure 'git am --abort return failed exit status when it fails' '
+test_expect_success 'git am --abort return failed exit status when it fails' '
 	test_when_finished "rm -rf file-2/ && git reset --hard && git am --abort" &&
 	git checkout changes &&
 	git format-patch -1 --stdout conflicting >changes.mbox &&