builtin-checkout.c: check error return from read_cache()

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-checkout.c

@@ -228,7 +228,8 @@ static int checkout_paths(struct tree *source_tree, const char **pathspec,
 	struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 
 	newfd = hold_locked_index(lock_file, 1);
-	read_cache();
+	if (read_cache() < 0)
+		return error("corrupt index file");
 
 	if (source_tree)
 		read_tree_some(source_tree, pathspec);
@@ -371,7 +372,9 @@ static int merge_working_tree(struct checkout_opts *opts,
 	int ret;
 	struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 	int newfd = hold_locked_index(lock_file, 1);
-	read_cache();
+
+	if (read_cache() < 0)
+		return error("corrupt index file");
 
 	if (opts->force) {
 		ret = reset_tree(new->commit->tree, opts, 1);