Fix crash in propsheet.c

[Keldon Jones]

Hi,

	I have an app (Garmin Mapsource) that crashes in
comctl32/propsheet.c.  The following patch fixes it, though I'm
not completely sure it's the right thing to do.

	Keldon


Changelog:
	Check return value of GetPropW before dereferencing it.


--- dlls/comctl32/propsheet.c   24 Jan 2003 00:54:59 -0000      1.81
+++ dlls/comctl32/propsheet.c   2 Feb 2003 17:47:51 -0000
@@ -2817,7 +2817,7 @@
                                                         PropSheetInfoStr);
       HWND hwndPage = 0;
 
-      if (psInfo->activeValid && psInfo->active_page != -1)
+      if (psInfo && psInfo->activeValid && psInfo->active_page != -1)
         hwndPage = psInfo->proppage[psInfo->active_page].hwndPage;
 
       SetWindowLongW(hwnd, DWL_MSGRESULT, (LONG)hwndPage);