Be more explicit about resetting Orderer state on prop change.

This only (to the best of my knowledge) gets called when moving between
multiple Orderer items in Perseus One, in which case this.state.current
gets set to []. But that assumption may change at some point, and since
we set this.state.current equal to this.props.current in getInitialState,
we should do the same here.

Test Plan:
Moved between two Orderer-weilding items in Perseus One, verified that
state was correctly reset. (No change from previous commit.)

Auditors: jack