Fix margin call on expired position.
Fix margin call on expired position.

The while loop was supposed to iterate over all cover positions looking
for expired orders to force them to cover. This is not the most
effecient approach, but it will work.

jakeporter/Bitshares,FollowMyVote/bitshares,bitshares/bitshares,bitshares/devshares,bitshares/bitshares,bitshares/devshares,frrp/bitshares,dacsunlimited/dac_play,camponez/bitshares,frrp/bitshares,bitsuperlab/cpp-play,bitshares/devshares,dacsunlimited/dac_play,frrp/bitshares,dacsunlimited/dac_play,bitshares/bitshares-0.x,jakeporter/Bitshares,dacsunlimited/dac_play,FollowMyVote/bitshares,bitshares/bitshares-0.x,bitshares/devshares,Ziftr/bitshares,Ziftr/bitshares,bitshares/bitshares,camponez/bitshares,RemitaBit/Remitabit,FollowMyVote/bitshares,jakeporter/Bitshares,bitshares/bitshares-0.x,RemitaBit/Remitabit,jakeporter/Bitshares,FollowMyVote/bitshares,bitshares/bitshares-0.x,bitshares/bitshares,bitsuperlab/cpp-play,jakeporter/Bitshares,bitshares/bitshares-0.x,bitsuperlab/cpp-play,RemitaBit/Remitabit,bitsuperlab/cpp-play,bitshares/devshares,bitshares/bitshares,bitshares/bitshares-0.x,Ziftr/bitshares,bitshares/bitshares,frrp/bitshares,frrp/bitshares,bitsuperlab/cpp-play,bitshares/devshares,FollowMyVote/bitshares,camponez/bitshares,camponez/bitshares,jakeporter/Bitshares,Ziftr/bitshares,dacsunlimited/dac_play,frrp/bitshares,camponez/bitshares,RemitaBit/Remitabit,dacsunlimited/dac_play,camponez/bitshares,RemitaBit/Remitabit,bitsuperlab/cpp-play,RemitaBit/Remitabit,FollowMyVote/bitshares