schema 1.1 commit: committing a minor fix to produce non null strings for XSD type names in error messages, when xsi:type attribute is used.

git-svn-id: https://svn.apache.org/repos/asf/xerces/java/branches/xml-schema-1.1-dev@1428373 13f79535-47bb-0310-9956-ffa450edef68