WSDL11Reader issue with schemas with no namespace and improve optimisation for circular references.

This is a continuation of JBWS-2411 where an optimisation was put in place to prevent an OutOfMemoryError caused by circular schema includes.

The change introduced a side effect and if subsequent imports or includes are found for the same schema as the processing is skipped because it has been performed once before the update of the schema location is also skipped.

At the same time schemas with no target namespace are also silently dropped so if these are required by the referenced schemas further parsing will result in numerous errors being reported.