mshtml: Make cookie parameter optional in ConnectionPoint_Advise.

dlls/mshtml/conpoint.c

@@ -158,7 +158,8 @@ static HRESULT WINAPI ConnectionPoint_Advise(IConnectionPoint *iface, IUnknown *
     }
 
     This->sinks[i].unk = sink;
-    *pdwCookie = i+1;
+    if(pdwCookie)
+        *pdwCookie = i+1;
 
     if(!i && This->data && This->data->on_advise)
         This->data->on_advise(This->container->outer, This->data);

dlls/mshtml/tests/htmldoc.c

@@ -4790,6 +4790,10 @@ static void test_ConnectionPoint(IConnectionPointContainer *container, REFIID ri
     if(IsEqualGUID(&IID_IPropertyNotifySink, riid)) {
         hres = IConnectionPoint_Advise(cp, (IUnknown*)&PropertyNotifySink, &cookie);
         ok(hres == S_OK, "Advise failed: %08x\n", hres);
+        hres = IConnectionPoint_Unadvise(cp, cookie);
+        ok(hres == S_OK, "Unadvise failed: %08x\n", hres);
+        hres = IConnectionPoint_Advise(cp, (IUnknown*)&PropertyNotifySink, NULL);
+        ok(hres == S_OK, "Advise failed: %08x\n", hres);
     } else if(IsEqualGUID(&IID_IDispatch, riid)) {
         hres = IConnectionPoint_Advise(cp, (IUnknown*)&EventDispatch, &cookie);
         ok(hres == S_OK, "Advise failed: %08x\n", hres);