ole32: Return the buffer pointer when WdtpInterfacePointer_UserMarshal fails.

dlls/ole32/tests/usrmarshal.c

@@ -576,6 +576,7 @@ static void marshal_WdtpInterfacePointer(DWORD umcb_ctx, DWORD ctx)
     ok(size == 0, "size should be 0 bytes, not %d\n", size);
     buffer = HeapAlloc(GetProcessHeap(), 0, size);
     buffer_end = WdtpInterfacePointer_UserMarshal(&umcb.Flags, ctx, buffer, unk, &IID_IUnknown);
+    ok(buffer_end == buffer, "buffer_end %p buffer %p\n", buffer_end, buffer);
     HeapFree(GetProcessHeap(), 0, buffer);
 
     /* Now for a non-NULL pointer. The marshalled data are two size DWORDS and then

dlls/ole32/usrmarshal.c

@@ -1641,7 +1641,7 @@ unsigned char * WINAPI WdtpInterfacePointer_UserMarshal(ULONG *pFlags, ULONG Rea
     if(CoMarshalInterface(stm, riid, punk, LOWORD(RealFlags), NULL, MSHLFLAGS_NORMAL) != S_OK)
     {
         IStream_Release(stm);
-        return NULL;
+        return pBuffer;
     }
 
     ALIGN_POINTER(pBuffer, 3);