V921-007 Check number of items in the list too.

Change-Id: I8908c554ea13a7896d0c63b2b19ec42126c60cb4
(cherry picked from commit 788acc5)

Author: godunko

dom/dom-core-nodes.adb

@@ -244,7 +244,7 @@ package body DOM.Core.Nodes is
    function First_Child (N : Node) return Node is
       List : constant Node_List := Child_Nodes (N);
    begin
-      if List.Items = null then
+      if List.Items = null or List.Last < 0 then
          return null;
       else
          return List.Items (0);
@@ -258,7 +258,7 @@ package body DOM.Core.Nodes is
    function Last_Child (N : Node) return Node is
       List : constant Node_List := Child_Nodes (N);
    begin
-      if List.Items = null then
+      if List.Items = null or List.Last < 0 then
          return null;
       else
          return List.Items (List.Last);