[BUG] Check for duplicate operator key when processing ProUpReg txes
[BUG] Check for duplicate operator key when processing ProUpReg txes

Otherwise a block with two protx using the same key could be accepted
and then cause an assertion failure in AddUniqueProperty.
Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX