[PATCH 0/1] MR6482: win32u: Leave window surface alpha bits to -1 when unset.

[Rémi Bernon (＠rbernon)]

Fixes: 05d727a935b9009f188cc74ca77e14afc44aef30
Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=57160