ServiceContainerEndpointRegistry#getRegisteredEndpoints() returns set containing null

The ServiceContainerEndpointRegistry#getRegisteredEndpoints() can return a set containing null as the retrieval of the service list from the container service registry plus the lookup of each service corresponding to the name is not atomic. We need to protect against this, as the consumers of org.jboss.wsf.spi.management.EndpointRegistry#resolve(EndpointResolver resolver) choke on it with NPEs.