[xml] addSibling missing check for element equality

[Kris Breuker <kris b-lex nl>]

Hello,

The functions xmlAddNextSibling and xmlAddPrevSibling have a check which 
checks if the element to be added is the same as the reference element. 
xmlAddSibling however does not have such a check, resulting in the loss 
of the element (the call to xmlUnlinkNode(elem) will unlink cur). I 
think the equality check should be added to addSibling as well, like in 
the attached patch.

Regards,
Kris Breuker

--- tree.c      Sat Jan 17 14:45:34 2009
+++ tree_patched.c      Wed Mar 11 12:16:22 2009
@@ -3103,6 +3103,14 @@
        return(NULL);
     }
 
+    if (cur == elem) {
+#ifdef DEBUG_TREE
+        xmlGenericError(xmlGenericErrorContext,
+               "xmlAddSibling : cur == elem\n");
+#endif
+       return(NULL);
+    }
+
     /*
      * Constant time is we can rely on the ->parent->last to find
      * the last sibling.