fix loading to use and return layer tree

fcore/parser/parser.sml

@@ -42,7 +42,7 @@ struct
                  (tl, canvasWidth, canvasHeight, tree, 1)
              in
                case tokens of
-                 [T.R_BRACE] => SOME tree
+                 [T.R_BRACE] => SOME (canvasWidth, canvasHeight, tree)
                | _ => NONE
              end
          | _ => NONE)