make sure htmlCtxtReset do reset the disableSAX field

As pointed out by Stefan Behnel <stefan_ml@behnel.de>
diff --git a/HTMLparser.c b/HTMLparser.c
index d51abe3..04bfbd4 100644
--- a/HTMLparser.c
+++ b/HTMLparser.c
@@ -6451,6 +6451,7 @@
 
     ctxt->wellFormed = 1;
     ctxt->nsWellFormed = 1;
+    ctxt->disableSAX = 0;
     ctxt->valid = 1;
     ctxt->vctxt.userData = ctxt;
     ctxt->vctxt.error = xmlParserValidityError;