msxml3: Check parameters of IXMLDOMNode::insertBefore()

[Paul Chitescu]

Changelog: msxml3: Check parameters of IXMLDOMNode::insertBefore() and return 
E_INVALIDARG if they are NULL as specified in MSDN.

This fixes Messenger crashing when clicking link to log in to a SIP account.
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--- ./dlls/msxml3/node.c	5 Oct 2006 10:04:36 -0000	1.33
+++ ./dlls/msxml3/node.c	2 Nov 2006 08:41:52 -0000
@@ -386,6 +386,9 @@
 
     TRACE("(%p)->(%p,var,%p)\n",This,newChild,outNewChild);
 
+    if (!(newChild && outNewChild))
+        return E_INVALIDARG;
+
     switch(V_VT(&refChild))
     {
     case VT_EMPTY: