Don't try to access an optional parameter if it is NULL

Modified: trunk/reactos/lib/setupapi/devinst.c

--- trunk/reactos/lib/setupapi/devinst.c	2005-11-15 06:14:31 UTC (rev 19241)
+++ trunk/reactos/lib/setupapi/devinst.c	2005-11-15 08:27:38 UTC (rev 19242)
@@ -1236,7 +1236,7 @@

     DWORD dwLength;
     DWORD rc;
 

-    if (IsEqualIID(class, &GUID_NULL))

+    if (class && IsEqualIID(class, &GUID_NULL))

         class = NULL;
 
     /* Open Enum key */