don't lock the screen dc if it's NULL

reactos/subsys/win32k/objects

diff -u -r1.49 -r1.50
--- cursoricon.c	26 Feb 2004 22:23:55 -0000	1.49
+++ cursoricon.c	27 Feb 2004 10:08:21 -0000	1.50
@@ -16,7 +16,7 @@

  *  along with this program; if not, write to the Free Software
  *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */

-/* $Id: cursoricon.c,v 1.49 2004/02/26 22:23:55 weiden Exp $ */

+/* $Id: cursoricon.c,v 1.50 2004/02/27 10:08:21 weiden Exp $ */

 
 #undef WIN32_LEAN_AND_MEAN
 

@@ -107,6 +107,7 @@

    PSURFOBJ soMask = NULL, soColor = NULL;
    PXLATEOBJ XlateObj = NULL;
    RECTL PointerRect;

+   HDC Screen;

   
    CurInfo = &WinStaObject->SystemCursor;
    OldCursor = CurInfo->CurrentCursorObject;

@@ -121,8 +122,12 @@

    }
   
    {

+      if(!(Screen = IntGetScreenDC()))
+      {
+        return (HCURSOR)0;
+      }

       /* FIXME use the desktop's HDC instead of using ScreenDeviceContext */

-      PDC dc = DC_LockDc(IntGetScreenDC());

+      PDC dc = DC_LockDc(Screen);

 
       if (!dc)
       {

@@ -132,7 +137,7 @@

       SurfObj = (PSURFOBJ)AccessUserObject((ULONG) dc->Surface);
       SurfGDI = (PSURFGDI)AccessInternalObject((ULONG) dc->Surface);
       DevInfo = dc->DevInfo;

-      DC_UnlockDc(IntGetScreenDC());

+      DC_UnlockDc(Screen);

    }
   
    if (!NewCursor && (CurInfo->CurrentCursorObject || ForceChange))