coverity#735810 Dereference after null check

Change-Id: I005ae6bf505fd2131c06e889f9fc3c12dae23c64

sc/source/ui/docshell/docsh4.cxx

@@ -2062,8 +2062,8 @@ void ScDocShell::GetPageOnFromPageStyleSet( const SfxItemSet* pStyleSet,
     }
 
     OSL_ENSURE( pStyleSet, "PageStyle-Set not found! :-(" );
-
-
+    if (!pStyleSet)
+        return;
 
     const SvxSetItem*   pSetItem = NULL;
     const SfxItemSet*   pSet     = NULL;