Fixing assorted potential problems raised by scan

* encoding.c parser.c relaxng.c runsuite.c tree.c xmlreader.c
  xmlschemas.c: nothing really serious but better safe than sorry
diff --git a/xmlreader.c b/xmlreader.c
index 1e562c2..c2afac7 100644
--- a/xmlreader.c
+++ b/xmlreader.c
@@ -1436,7 +1436,7 @@
 	/*
 	 * Cleanup of the old node
 	 */
-	if ((reader->preserves == 0) &&
+	if ((oldnode != NULL) && (reader->preserves == 0) &&
 #ifdef LIBXML_XINCLUDE_ENABLED
 	    (reader->in_xinclude == 0) &&
 #endif