fix: validator args unexpectedly unbound

closes #852

examples/acceptance_tests/096/validators/foo.ak

@@ -0,0 +1,7 @@
+use aiken/transaction.{ScriptContext}
+
+validator {
+  fn is_fourty_two(dat, rdm, _ctx: ScriptContext) -> Bool {
+    rdm == dat && #"68656c6c6f20776f726c64" == #"68656c6c6f20776f726c64"
+  }
+}