Guard against division by zero for reindex zerocoin/accumulators

in the event that the local chainActive is equal or below that of the
relevant zerocoin block heights, there is nothing to do, so bypass
the internal process.

Author: Fuzzbawls

src/init.cpp

@@ -1437,11 +1437,13 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
 
                 // Drop all information from the zerocoinDB and repopulate
                 if (GetBoolArg("-reindexzerocoin", false)) {
-                    uiInterface.InitMessage(_("Reindexing zerocoin database..."));
-                    std::string strError = ReindexZerocoinDB();
-                    if (strError != "") {
-                        strLoadError = strError;
-                        break;
+                    if (chainActive.Height() > Params().Zerocoin_StartHeight()) {
+                        uiInterface.InitMessage(_("Reindexing zerocoin database..."));
+                        std::string strError = ReindexZerocoinDB();
+                        if (strError != "") {
+                            strLoadError = strError;
+                            break;
+                        }
                     }
                 }
 
@@ -1456,11 +1458,14 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
 
                 // Force recalculation of accumulators.
                 if (GetBoolArg("-reindexaccumulators", false)) {
-                    CBlockIndex* pindex = chainActive[Params().Zerocoin_StartHeight()];
-                    while (pindex->nHeight < chainActive.Height()) {
-                        if (!count(listAccCheckpointsNoDB.begin(), listAccCheckpointsNoDB.end(), pindex->nAccumulatorCheckpoint))
-                            listAccCheckpointsNoDB.emplace_back(pindex->nAccumulatorCheckpoint);
-                        pindex = chainActive.Next(pindex);
+                    if (chainActive.Height() > Params().Zerocoin_Block_V2_Start()) {
+                        CBlockIndex *pindex = chainActive[Params().Zerocoin_Block_V2_Start()];
+                        while (pindex->nHeight < chainActive.Height()) {
+                            if (!count(listAccCheckpointsNoDB.begin(), listAccCheckpointsNoDB.end(),
+                                       pindex->nAccumulatorCheckpoint))
+                                listAccCheckpointsNoDB.emplace_back(pindex->nAccumulatorCheckpoint);
+                            pindex = chainActive.Next(pindex);
+                        }
                     }
                 }
 

src/main.cpp

@@ -2760,8 +2760,8 @@ bool RecalculatePIVSupply(int nHeightStart)
 bool ReindexAccumulators(list<uint256>& listMissingCheckpoints, string& strError)
 {
     // PIVX: recalculate Accumulator Checkpoints that failed to database properly
-    uiInterface.ShowProgress(_("Calculating missing accumulators..."), 0);
-    if (!listMissingCheckpoints.empty() && chainActive.Height() >= Params().Zerocoin_StartHeight()) {
+    if (!listMissingCheckpoints.empty()) {
+        uiInterface.ShowProgress(_("Calculating missing accumulators..."), 0);
         LogPrintf("%s : finding missing checkpoints\n", __func__);
 
         //search the chain to see when zerocoin started