made lastBlock AtomicReference
made lastBlock AtomicReference

duckx/nxt,duckx/nxt,Ziftr/nxt,fimkrypto/nxt,duckx/nxt,dmkaplan2000/nxt_dmk,metrospark/czarcraft,metrospark/czarcraft,metrospark/czarcraft,fimkrypto/nxt,dmkaplan2000/nxt_dmk,fimkrypto/nxt,Ziftr/nxt,fimkrypto/nxt,dmkaplan2000/nxt_dmk,Ziftr/nxt