Commit 8cd69810596e ("msi: Get system directory just once.") remove call to GetSystemDirectoryW() in load_fusion_dlls() but forgot to add corresponding wcscpy() call. This causes loading mscoree.dll to fail, breaking .NET-assembly-related functionalities. Add it back.
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Note: it seems like there isn't a test which actually test interactions between msi.dll and GAC/WinSxS. It probably makes sense to add some or modify existing ones.
-- v2: msi: fix .NET assembly-related functionalities due to missed string copy