Address XML_Parse return type mis-match warning (issue #512)

(Function XML_Parse returns enum XML_Status, not enum XML_Error.)
diff --git a/expat/lib/xmlparse.c b/expat/lib/xmlparse.c
index 97ef730..3491811 100644
--- a/expat/lib/xmlparse.c
+++ b/expat/lib/xmlparse.c
@@ -1550,7 +1550,7 @@
   else if (bufferPtr == bufferEnd) {
     const char *end;
     int nLeftOver;
-    enum XML_Error result;
+    enum XML_Status result;
     parseEndByteIndex += len;
     positionPtr = s;
     ps_finalBuffer = (XML_Bool)isFinal;