fix DIP0001 implementation (#1639)

According to DIP0001 description we should be using payment queue to select current masternode:
>As a block is mined the version number is determined by the miner who mined it and the masternode that is selected for that block.
>...
>The selection of a round consisting of 4032 blocks is made based on masternodes not being randomly selected, rather they are in a queue.

https://github.com/dashpay/dips/blob/master/dip-0001.md

src/masternodeman.cpp

@@ -460,6 +460,19 @@ bool CMasternodeMan::GetMasternodeInfo(const CPubKey& pubKeyMasternode, masterno
     return false;
 }
 
+bool CMasternodeMan::GetMasternodeInfo(const CScript& payee, masternode_info_t& mnInfoRet)
+{
+    LOCK(cs);
+    for (auto& mnpair : mapMasternodes) {
+        CScript scriptCollateralAddress = GetScriptForDestination(mnpair.second.pubKeyCollateralAddress.GetID());
+        if (scriptCollateralAddress == payee) {
+            mnInfoRet = mnpair.second.GetInfo();
+            return true;
+        }
+    }
+    return false;
+}
+
 bool CMasternodeMan::Has(const COutPoint& outpoint)
 {
     LOCK(cs);

src/masternodeman.h

@@ -162,8 +162,8 @@ class CMasternodeMan
     bool Has(const COutPoint& outpoint);
 
     bool GetMasternodeInfo(const COutPoint& outpoint, masternode_info_t& mnInfoRet);
-
     bool GetMasternodeInfo(const CPubKey& pubKeyMasternode, masternode_info_t& mnInfoRet);
+    bool GetMasternodeInfo(const CScript& payee, masternode_info_t& mnInfoRet);
 
     /// Find an entry in the masternode list that is next to be paid
     bool GetNextMasternodeInQueueForPayment(int nBlockHeight, bool fFilterSigTime, int& nCountRet, masternode_info_t& mnInfoRet);

src/validation.cpp

@@ -1885,10 +1885,18 @@ int32_t ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Para
         ThresholdState state = VersionBitsState(pindexPrev, params, pos, versionbitscache);
         const struct BIP9DeploymentInfo& vbinfo = VersionBitsDeploymentInfo[pos];
         if (vbinfo.check_mn_protocol && state == THRESHOLD_STARTED && !fAssumeMasternodeIsUpgraded) {
+            CScript payee;
             masternode_info_t mnInfo;
-            bool fFound = mnodeman.GetMasternodeByRank(1, mnInfo, pindexPrev->nHeight);
-            if (!fFound || mnInfo.nProtocolVersion < PROTOCOL_VERSION) {
-                // no masternodes(?) or masternode is not upgraded yet
+            if (!mnpayments.GetBlockPayee(pindexPrev->nHeight + 1, payee)) {
+                // no votes for this block
+                continue;
+            }
+            if (!mnodeman.GetMasternodeInfo(payee, mnInfo)) {
+                // unknown masternode
+                continue;
+            }
+            if (mnInfo.nProtocolVersion < DIP0001_PROTOCOL_VERSION) {
+                // masternode is not upgraded yet
                 continue;
             }
         }

src/validation.h

@@ -163,6 +163,8 @@ extern bool fAlerts;
 extern bool fEnableReplacement;
 
 extern std::map<uint256, int64_t> mapRejectedBlocks;
+
+static const int DIP0001_PROTOCOL_VERSION = 70208;
 extern std::atomic<bool> fDIP0001LockedInAtTip;
 extern std::atomic<bool> fDIP0001ActiveAtTip;