Add support for unless

ifs without a true branch would crash before
Somewhat more verbose but unified

test/vool/test_if_no_if.rb

@@ -0,0 +1,31 @@
+
+require_relative "helper"
+
+module Vool
+  class TestIfNoIf < MiniTest::Test
+    include VoolCompile
+
+    def setup
+      Parfait.boot!(Parfait.default_test_options)
+      @compiler = compile_first_method( "unless(@a) ; @a = 5 ; end")
+      @ins = @compiler.mom_instructions.next
+    end
+
+    def test_condition_compiles_to_check
+      assert_equal TruthCheck , @ins.class , @ins
+    end
+    def test_condition_is_slot
+      assert_equal SlotDefinition , @ins.condition.class , @ins
+    end
+    def test_label_after_check
+      assert_equal Label , @ins.next.class , @ins
+    end
+    def test_label_last
+      assert_equal Label , @ins.last.class , @ins
+    end
+    def test_array
+      check_array  [TruthCheck, Label, Jump, Label, SlotLoad ,
+                    Label, Label, ReturnSequence, Label] , @ins
+    end
+  end
+end