Add some padding in WINPROC_wrapper

[Mike McCormack]

Uwe Bonnes wrote:
> Changelog
> 	windows/winproc.c: WINPROC_wrapper
> 	Add some padding between saved registers and the winproc
> 	arguments. Some winprocs may trash the register area.
> 
> As Mike Hearn suggested, adding some padding helped with my problem with
> WebPACK_42wp30_full_installer.exe. I hope, I found the right way to add that
> padding.

It may work for one application, but it doesn't look like a propper fix. 
  I'd suggest there's probably something else going on that's causing 
stack corruption.

Mike