user[3/5]: handle special cases for SPI_SETDESKWALLPAPER

[Andrey Turkin]

I cannot see where emptyW initialized.

Andrew Ziem wrote:
> The special cases remove the wallpaper or set it to default.  
> Previously, these cases were ignored, so Wine would crash.
>
<snip>
> +        if (NULL == pvParam || SETWALLPAPER_DEFAULT == pvParam)
> +        {
> +            static const WCHAR emptyW[1];
> +            if (!SetDeskWallPaper( (LPSTR)pvParam ))
> +                return FALSE;
> +            SYSPARAMS_Save(SPI_SETDESKWALLPAPER_REGKEY, SPI_SETDESKWALLPAPER_VALNAME, emptyW, fWinIni);
> +        }
> +        else
> +        {
> +            if (!SetDeskWallPaper( (LPSTR) pvParam ))
> +               return FALSE;
> +        }
> +        break;
>