Removed unnecessary null check.

Libs/PluginFramework/ctkServiceReference.cpp

@@ -61,7 +61,7 @@ ctkServiceReference& ctkServiceReference::operator=(int null)
 {
   if (null == 0)
   {
-    if (d_func() && !d_func()->ref.deref())
+    if (!d_func()->ref.deref())
       delete d_ptr;
     d_ptr = new ctkServiceReferencePrivate(0);
   }