shell32: make sure BrowseForFolder doesn't return NULL for the Desktop folder as this means a cancel (should fix bug #5533)

[Mikołaj Zalewski]

> This function is a bit ugly. It seems this policy should be made in 
> the BrsFolder_OnCommand function, rather than in pidl.c as a file.

  Yes, after I've found _ILCreateDesktop there is no need for a helper 
funciton. I'll send a patch without it.

Mikolaj Zalewski