added optional maxlen argument to NLMSALetters() constructor added protection against using NULL pointers in various places
added optional maxlen argument to NLMSALetters() constructor
added protection against using NULL pointers in various places

ctb/pygr,cjlee112/pygr,ctb/pygr,cjlee112/pygr,theoryno3/pygr,GenDataPro/pygr,theoryno3/pygr,ctb/pygr,RitwikGupta/pygr,RitwikGupta/pygr,RitwikGupta/pygr,ctb/pygr,theoryno3/pygr,GenDataPro/pygr,ctb/pygr,cjlee112/pygr,GenDataPro/pygr,cjlee112/pygr