PsGetWin32Process() == NULL crash

(This bug appered ~ Oct 10)

Somehow when the code gets in IntGetWindowObject and calls PsGetWin32Process
it crashes because PsGetWin32Process() == NULL and it dereferences it. I can't
give a complete backtrace, but it happens in many places. My take is that it's
caused by something in callbacks.

Reproducing is really easy and there are many methods how to do that:
1) Run sol.exe from Win XP. It carses on start.
2) Run taskmgr.exe and try to resize window.
3) ...

Filip