message: Fix invisible group mobs bug
  This is a simplified adaptation of
  from Retrobution.
diff: @@ -98,11 +98,17 @@ void MobAI::groupRetreat(Mob *mob) {
  }
  Mob* followerMob = (Mob*)NPCManager::NPCs[leadMob->groupMember[i]];
  + if (followerMob->state != MobState::COMBAT)
  + continue;
  +
  followerMob->target = nullptr;
  followerMob->state = MobState::RETREAT;
  clearDebuff(followerMob);
  }
  + if (leadMob->state != MobState::COMBAT)
  + return;
  +
  leadMob->target = nullptr;
  leadMob->state = MobState::RETREAT;
  clearDebuff(leadMob);
  