discodex: make map_reader = None explicit for DiscoDBIterator
discodex: make map_reader = None explicit for DiscoDBIterator

pavlobaron/disco_playground,pooya/disco,discoproject/disco,mozilla/disco,ErikDubbelboer/disco,beni55/disco,simudream/disco,beni55/disco,oldmantaiter/disco,pavlobaron/disco_playground,seabirdzh/disco,simudream/disco,simudream/disco,simudream/disco,ErikDubbelboer/disco,discoproject/disco,ktkt2009/disco,mozilla/disco,oldmantaiter/disco,mwilliams3/disco,beni55/disco,mwilliams3/disco,oldmantaiter/disco,seabirdzh/disco,beni55/disco,oldmantaiter/disco,mwilliams3/disco,scrapinghub/disco,pombredanne/disco,mwilliams3/disco,simudream/disco,mozilla/disco,ErikDubbelboer/disco,pooya/disco,ktkt2009/disco,scrapinghub/disco,pombredanne/disco,ktkt2009/disco,ErikDubbelboer/disco,scrapinghub/disco,pavlobaron/disco_playground,mwilliams3/disco,discoproject/disco,pavlobaron/disco_playground,ErikDubbelboer/disco,ktkt2009/disco,ktkt2009/disco,pombredanne/disco,pombredanne/disco,pooya/disco,beni55/disco,seabirdzh/disco,seabirdzh/disco,pooya/disco,scrapinghub/disco,seabirdzh/disco,pombredanne/disco,discoproject/disco,discoproject/disco,oldmantaiter/disco,mozilla/disco