win32k: regional settings window in 2nd stage crashes when being closed by mouse click

This bug has been regress-tested to rev. 52136: http://svn.reactos.org/svn/reactos?view=rev&revision=52136

To reproduce, open any of the two regional settings/keyboard windows then close them with mouse click. This bug might also be triggered by opening window and closing it with keyboard shortcuts (s/esc) while moving mouse cursor over the settings window. The crash follows:

(subsystems\win32\win32k\ntuser\vis.c:71) ATM the Current Window or Parent is dead!
Entered debugger on last-chance exception (Exception Code: 0xc0000005) (Page Fault)
Memory at 0x00000030 could not be read: Page not present.
kdb:> bt
Eip:
<win32k.sys:71e78 (subsystems/win32/win32k/ntuser/msgqueue.c:88 (@UserSetCursor@8))>
Frames:
<win32k.sys:5cdfb (subsystems/win32/win32k/ntuser/cursoricon.c:302 (@IntDestroyCurIconObject@8))>
<win32k.sys:5ceb1 (subsystems/win32/win32k/ntuser/cursoricon.c:345 (@IntCleanupCurIcons@8))>
<win32k.sys:3f521 (subsystems/win32/win32k/main/dllmain.c:167 (Win32kProcessCallback@8))>
<ntoskrnl.exe:e3abf (ntoskrnl/ps/kill.c:700 (PspExitThread@4))>
<ntoskrnl.exe:e3f4b (ntoskrnl/ps/kill.c:967 (PspTerminateThreadByPointer@12))>
<ntoskrnl.exe:e439e (ntoskrnl/ps/kill.c:1199 (NtTerminateProcess@8))>
<ntoskrnl.exe:758c (ntoskrnl/ke/i386/traphdlr.c:1587 (@KiFastCallEntryHandler@8))>
<ntoskrnl.exe:fb9c9 (ntoskrnl\ke\i386\trap.s:135 (KiFastCallEntry))>
<ntdll.dll:b799>
<msvcrt.dll:c39f>
<msvcrt.dll:c3c9>
<rundll32.exe:1cac>