ole32/tests: make sure to use a return value (LLVM/Clang)

[Austin English]

-- 
-Austin
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diff --git a/dlls/ole32/tests/marshal.c b/dlls/ole32/tests/marshal.c
index 87b2006..33e074c 100644
--- a/dlls/ole32/tests/marshal.c
+++ b/dlls/ole32/tests/marshal.c
@@ -1870,6 +1870,7 @@ static LRESULT CALLBACK window_proc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM l
         /* note the use of the magic IID_IWineTest value to tell remote thread
          * to try to send a message back to us */
         hr = IClassFactory_CreateInstance(proxy, NULL, &IID_IWineTest, (void **)&object);
+        ok(hr == S_FALSE, "expected S_FALSE, got %d\n", hr);
 
         IClassFactory_Release(proxy);