Fixed SEGV caused by commit 6be04664 when creating universal slots.

Signed-off-by: Michele Calgaro <michele.calgaro@yahoo.it>

sip/qt/qobject.sip

@@ -1414,7 +1414,7 @@ static void *sipTQtCreateUniversalSlot(sipWrapper *tx, const char *sig,
     pyqt3SlotConnection conn;
 
     /* Initialise the connection. */
-    if (sipGetAddress(&tx->super) == NULL)
+    if (tx && sipGetAddress(&tx->super) == NULL)
     {
         conn.sc_transmitter = 0;
     }