Merge branch 'jk/clone-copy-alternates-fix' into maint

"git clone" of a local repository can be done at the filesystem
level, but the codepath did not check errors while copying and
adjusting the file that lists alternate object stores.

* jk/clone-copy-alternates-fix:
  clone: detect errors in normalize_path_copy

builtin/clone.c

@@ -355,8 +355,11 @@ static void copy_alternates(struct strbuf *src, struct strbuf *dst,
 			continue;
 		}
 		abs_path = mkpathdup("%s/objects/%s", src_repo, line.buf);
-		normalize_path_copy(abs_path, abs_path);
-		add_to_alternates_file(abs_path);
+		if (!normalize_path_copy(abs_path, abs_path))
+			add_to_alternates_file(abs_path);
+		else
+			warning("skipping invalid relative alternate: %s/%s",
+				src_repo, line.buf);
 		free(abs_path);
 	}
 	strbuf_release(&line);