Return early in IsBanned.
Return early in IsBanned.

I am not aware of any reason that we'd try to stop a ban-list timing
 side-channel and the prior code wouldn't be enough if we were.

Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX