fix field access extra this

NameNode.py

@@ -117,9 +117,10 @@ class NameNode(ASTNode):
             self.addToPrefix("contain")
 
             # evaluate THIS first, fieldnode will be added to prefixNodes in checkType()
-            cNameNode = genNameNode(self.typeName)
-            cNameNode.isThis = True
-            self.prefixNodes.append(cNameNode)
+            if not self.prefixNodes:
+                cNameNode = genNameNode(self.typeName)
+                cNameNode.isThis = True
+                self.prefixNodes.append(cNameNode)
 
             return True
         return False
@@ -242,7 +243,7 @@ class NameNode(ASTNode):
                             self.methodClass = meth.env.getNode(meth.typeName, 'type')
 
                         self.methodName = self.IDs[0]
-                        
+
                     else:
                         if curType.myType and curType.myType.isArray and self.IDs[0] == 'length':
                             self.myType = TypeStruct("int", None)