HORNETQ-578: Destroy CF with null bindings

https://issues.jboss.org/browse/HORNETQ-578

Fixes issue where calling destory on JMS Connection Factory was failing
silently when Connection Factory bindings was empty or set to null.
Merge pull request #1739 from mtaylor/destroy_cf_with_null_bindings

HORNETQ-578: Destroy CF with null bindings