WIXBUG:4609 - Fix incorrect use of BVariantCopy

Interesting. What if the source (`pValue`) is encrypted but the target (`pVariant`) is not? Is it best to propagate the encryption in that case? Given the subtleties of the encrypted handling, I think a header comment on these functions would be a good idea (kinda' like the Str functions have them since strings are a bit different in dutil).