win32u: Copy an incoming CB_GETCOMBOBOXINFO when packing it for the client.
The only important field at this point is cbSize, but if it's zero, the message will not be processed.
The other option would be to zero the buffer and then do the equivalent of ((COMBOBOXINFO *)buffer)->cbSize = sizeof(COMBOBOXINFO)
, rather than copying the incoming lparam. That doesn't seem better to me, but I'm no expert.