Register Xnest colormap screen private key

This key is used to store the currently installed colormap and must be
registered before we can use it.

Reviewed-by: Jamey Sharp <jamey@minilop.net>
Signed-off-by: Keith Packard <keithp@keithp.com>

hw/xnest/Color.c

@@ -469,6 +469,9 @@ xnestCreateDefaultColormap(ScreenPtr pScreen)
   unsigned short zero = 0, ones = 0xFFFF;  
   Pixel wp, bp;
 
+  if (!dixRegisterPrivateKey(&cmapScrPrivateKeyRec, PRIVATE_SCREEN, 0))
+      return FALSE;
+
   for (pVisual = pScreen->visuals;
        pVisual->vid != pScreen->rootVisual;
        pVisual++);