Fix FTBFS with stricter C++11

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit f60d0e12e9)

superkaramba/src/imagelabel_python.cpp

@@ -122,7 +122,7 @@ PyObject* py_createTaskIcon(PyObject *, PyObject *args)
   {
     //no task was found
     tqWarning("Task not found.");
-    return (long)NULL ;
+    return NULL;
   }
   //retrieve the TQPixmap that represents this image
   TQPixmap iconPixmap = KWin::icon(currTask->window());