Checking whether variables have types before accessing them in the PDDL translator.

tests/data/issues/issue-4.pddl

@@ -0,0 +1,11 @@
+(define (domain tsp)
+(:requirements :negative-preconditions)
+  (:predicates
+     (at ?x)
+     (visited ?x)
+      (connected ?x ?y))
+
+  (:action move
+	:parameters (?x ?y)
+	:precondition (and (at ?x) (not (visited ?y)) (connected ?x ?y))
+	:effect (and (at ?y) (visited ?y) (not (at ?x)))))