GuessVerificationProgress: cap the ratio to 1

The getblockchaininfo RPC call could sometime return a
'validationprogress' > 1, but this is absurd.

src/validation.cpp

@@ -5066,7 +5066,7 @@ double GuessVerificationProgress(const ChainTxData& data, const CBlockIndex *pin
         fTxTotal = pindex->nChainTx + (nNow - pindex->GetBlockTime()) * data.dTxRate;
     }
 
-    return pindex->nChainTx / fTxTotal;
+    return std::min<double>(pindex->nChainTx / fTxTotal, 1.0);
 }
 
 class CMainCleanup