OOP: fixed null reference as initial value for class variable (bug 563718)

Change-Id: Ice786f009708e01f7944c020b553fa63ff977ac5
Signed-off-by: Botond Baranyi <botond.baranyi@ericsson.com>

core/OOP.hh

@@ -91,6 +91,9 @@ public:
         TTCN_error("Invalid dynamic type of initial value.");
       }
     }
+    else {
+      ptr = NULL;
+    }
   }
   
   void clean_up() {

regression_test/oop/oop.ttcn

@@ -385,6 +385,10 @@ testcase tc_references() runs on CT {
   if (ispresent(v_null)) {
     setverdict(fail, "#17");
   }
+  var BaseClass v_base2 := v_null;
+  if (v_base2 != null) {
+    setverdict(fail, "#18");
+  }
   setverdict(pass);
 }