[FIX] trade: set default currency pair issuers to null on reset
[FIX] trade: set default currency pair issuers to null on reset

due to what appears to be an unused boolean 'keepPair' that
defaulted to false, issuers of the currency pair were being
set to the id.account_id, resulting in subscriptions to the
wrong order books.

xdv/ripple-client-desktop,yongsoo/ripple-client,dncohen/ripple-client-desktop,ripple/ripple-client,darkdarkdragon/ripple-client,arturomc/ripple-client,MatthewPhinney/ripple-client-desktop,ripple/ripple-client,thics/ripple-client-desktop,thics/ripple-client-desktop,h0vhannes/ripple-client,yongsoo/ripple-client-desktop,ripple/ripple-client-desktop,darkdarkdragon/ripple-client,mrajvanshy/ripple-client-desktop,xdv/ripple-client,xdv/ripple-client,yxxyun/ripple-client-desktop,MatthewPhinney/ripple-client,MatthewPhinney/ripple-client-desktop,h0vhannes/ripple-client,wangbibo/ripple-client,xdv/ripple-client-desktop,darkdarkdragon/ripple-client,mrajvanshy/ripple-client,h0vhannes/ripple-client,yongsoo/ripple-client,wangbibo/ripple-client,wangbibo/ripple-client,ripple/ripple-client,ripple/ripple-client-desktop,Madsn/ripple-client,MatthewPhinney/ripple-client,arturomc/ripple-client,arturomc/ripple-client,yongsoo/ripple-client,xdv/ripple-client,vhpoet/ripple-client,yxxyun/ripple-client-desktop,bankonme/ripple-client-desktop,ripple/ripple-client,vhpoet/ripple-client-desktop,mrajvanshy/ripple-client,yongsoo/ripple-client-desktop,wangbibo/ripple-client,bsteinlo/ripple-client,vhpoet/ripple-client,Madsn/ripple-client,xdv/ripple-client,MatthewPhinney/ripple-client,yongsoo/ripple-client,darkdarkdragon/ripple-client-desktop,MatthewPhinney/ripple-client,bsteinlo/ripple-client,darkdarkdragon/ripple-client-desktop,bankonme/ripple-client-desktop,vhpoet/ripple-client,vhpoet/ripple-client-desktop,mrajvanshy/ripple-client,darkdarkdragon/ripple-client,mrajvanshy/ripple-client-desktop,xdv/ripple-client-desktop,Madsn/ripple-client,vhpoet/ripple-client,arturomc/ripple-client,mrajvanshy/ripple-client,Madsn/ripple-client,dncohen/ripple-client-desktop,h0vhannes/ripple-client