Utilities/Release: Stabilize include order in WiX custom action

In `detect_nsis_overwrite.cpp` we include windows.h first, and we must
preserve that.  Place the include in an isolated block so that tools
that sort includes do not move it.

Utilities/Release/WiX/CustomAction/detect_nsis_overwrite.cpp

 #include <windows.h>
+
 #include <msi.h>
 #include <msiquery.h>