exported xmlXPath{NAN,PINF,NINF} fixed xmlXPathNodeSetItem when passing


	* include/libxml/xpath.h: exported xmlXPath{NAN,PINF,NINF}
	  fixed xmlXPathNodeSetItem when passing index=0
diff --git a/include/libxml/xpath.h b/include/libxml/xpath.h
index 7a1ec75..87a6118 100644
--- a/include/libxml/xpath.h
+++ b/include/libxml/xpath.h
@@ -283,11 +283,15 @@
  * Objects and Nodesets handling
  */
 
+LIBXML_DLL_IMPORT extern double xmlXPathNAN;
+LIBXML_DLL_IMPORT extern double xmlXPathPINF;
+LIBXML_DLL_IMPORT extern double xmlXPathNINF;
+
 /* These macros may later turn into functions */
 #define xmlXPathNodeSetGetLength(ns) ((ns) ? (ns)->nodeNr : 0)
 #define xmlXPathNodeSetItem(ns, index)				\
 		((((ns) != NULL) && 				\
-		  ((index) > 0) && ((index) <= (ns)->nodeNr)) ?	\
+		  ((index) >= 0) && ((index) < (ns)->nodeNr)) ?	\
 		 (ns)->nodeTab[(index)]				\
 		 : NULL)