TokenizerChain methods may return null depending on how constructor is called -- causes NPE in luke request handler

TokenizerChain created using 2-arg constructor has null in charFilters, so LukeRequestHandler throws NPE on iterating it.

TokenizerChain constructor's should be hardened to do explicit null checks, throwing early NPE where appropriate (tokenizer factory), or initializing internal arrays to have 0 length when optional (factories for char filters and token filters)