parameter checking in CoMarshalInterface

[Aric Stewart]

Changlog: return an error if the IUnknown pointer is NULL and dont crash
tested with win2k and this is proper behavior
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Index: dlls/ole32/marshal.c
===================================================================
RCS file: /home/wine/wine/dlls/ole32/marshal.c,v
retrieving revision 1.19
diff -u -w -r1.19 marshal.c
--- dlls/ole32/marshal.c	17 Jun 2004 19:55:24 -0000	1.19
+++ dlls/ole32/marshal.c	29 Jun 2004 15:25:30 -0000
@@ -453,6 +453,10 @@
   TRACE("(%p, %s, %p, %lx, %p, %lx)\n",
     pStm,debugstr_guid(riid),pUnk,dwDestContext,pvDestContext,mshlflags
   );
+
+  if (pUnk == NULL)
+    return E_INVALIDARG;
+
   STUBMGR_Start(); /* Just to be sure we have one running. */
   mid.processid = GetCurrentProcessId();
   IUnknown_QueryInterface(pUnk,&IID_IUnknown,(LPVOID*)&pUnknown);