POS mining: handle error when trying to mine spent coins
POS mining: handle error when trying to mine spent coins

quark-project/quark,quark-project/quark,MaxGuevara/quark,MaxGuevara/quark,quark-project/quark,quark-project/quark,MaxGuevara/quark,MaxGuevara/quark,quark-project/quark,MaxGuevara/quark,quark-project/quark,MaxGuevara/quark