don't try to dereference NULL pointers

now Avira AntiVir installs without crashing the whole system

svn path=/trunk/; revision=34300

reactos/subsystems/win32/win32k/ntuser/message.c

@@ -1550,6 +1550,8 @@ co_IntDoSendMessage(HWND hWnd,
          MmCopyToCaller(UnsafeInfo, &Info, sizeof(NTUSERSENDMESSAGEINFO));
          return 0;
       }
+      if (!Window->Wnd)
+         return 0;
    }
 
    /* FIXME: Check for an exiting window. */

reactos/subsystems/win32/win32k/ntuser/monitor.c

@@ -899,6 +899,9 @@ NtUserMonitorFromWindow(
       RETURN(hMonitor);
    }
 
+   if (!Window->Wnd)
+      RETURN(hMonitor);
+
    Rect.left = Rect.right = Window->Wnd->WindowRect.left;
    Rect.top = Rect.bottom = Window->Wnd->WindowRect.bottom;