Enforce focus of the Wine Gecko download prompt on ReactOS' second stage install wizard

[APPWIZ][SYSSETUP]

Pass over the parent window reference down the appwiz.cpl addons installer.

Fixes the stray Wine Gecko download prompt window, enforcing its focus and avoiding accidentally hiding it behind the second stage install wizard when you click on that, which may confuse or annoy the user, blocking the installation flow or even forcing a manual reboot.

This was a pet peeve of mine, and nice for a first patch.

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Tested and working so far, without hacks.