use fake memory

fix integer offset bug
(which only didn’t cause errors as fixnums are still an order too big
and the famous +1 error hit the empty space)

test/risc/test_machine.rb

@@ -39,7 +39,7 @@ module Risc
     end
     def test_first_binary_jump
       bin = Parfait.object_space.get_init.binary
-      assert 0 != bin.get_word(14) , "index 0 is 0 #{bin.inspect}"
+      assert 0 != bin.get_word(Parfait::BinaryCode.data_length) , "index 0 is 0 #{bin.inspect}"
     end
     def test_second_binary_first
       bin = Parfait.object_space.get_init.binary.next