[libxml2] Fix a potential NULL dereference in tree code

[Daniel Veillard <veillard src gnome org>]

commit 75d13092f2886176fa8e8f354eb8a0e51f7409fd
Author: Daniel Veillard <veillard redhat com>
Date:   Wed Sep 11 15:11:27 2013 +0800

    Fix a potential NULL dereference in tree code
    
    https://bugzilla.gnome.org/show_bug.cgi?id=707750
    
    Also reported by Gaurav, simple fix to check the pointer before
    dereference

 tree.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/tree.c b/tree.c
index 7981771..b517a2c 100644
--- a/tree.c
+++ b/tree.c
@@ -9785,7 +9785,8 @@ leave_node:
            if (clone->parent != NULL)
                clone->parent->last = clone;
            clone = clone->parent;
-           parentClone = clone->parent;
+           if (clone != NULL)
+               parentClone = clone->parent;
            /*
            * Process parent --> next;
            */