use ctxt->standalone = -2 to indicate that the XMLDecl was parsed but no

* parser.c: use ctxt->standalone = -2 to indicate that the
  XMLDecl was parsed but no standalone attribute was found,
  suggested by Michael Day to detect if an XMLDecl was found.
Daniel
diff --git a/parser.c b/parser.c
index 5f561ee..66f8bd3 100644
--- a/parser.c
+++ b/parser.c
@@ -8901,6 +8901,13 @@
     xmlChar *version;
 
     /*
+     * This value for standalone indicates that the document has an
+     * XML declaration but it does not have a standalone attribute.
+     * It will be overwritten later if a standalone attribute is found.
+     */
+    ctxt->input->standalone = -2;
+
+    /*
      * We know that '<?xml' is here.
      */
     SKIP(5);