deal with http://bugzilla.validator.nu/show_bug.cgi?id=865

patch.parser.xmlns.1.diff

diff -r 5922374b5f63 src/nu/validator/gnu/xml/aelfred2/SAXDriver.java
--- a/src/nu/validator/gnu/xml/aelfred2/SAXDriver.java	Thu Dec 23 16:14:07 2010 +0900
+++ b/src/nu/validator/gnu/xml/aelfred2/SAXDriver.java	Tue Oct 18 16:44:42 2011 +0900
@@ -820,6 +820,8 @@
     }
 
     private void declarePrefix(String prefix, String uri) throws SAXException {
+        // NOTE: uri may be the empty string
+
         int index = uri.indexOf(':');
 
         // many versions of nwalsh docbook stylesheets
@@ -829,7 +831,7 @@
         }
 
         // char [0] must be ascii alpha [RFC 2396]
-        if (!isAlpha(uri.charAt(0))) {
+        if (uri.length() != 0 && !isAlpha(uri.charAt(0))) {
             fatal("First character of the URI must be ascii alpha");
         }