Bugfix: RPC/mining: Fail properly in estimatesmartfee if smart fee data is unavailable

src/rpc/mining.cpp

@@ -1121,10 +1121,10 @@ static RPCHelpMan estimatesmartfee()
     UniValue errors(UniValue::VARR);
     FeeCalculation feeCalc;
     CFeeRate feeRate{fee_estimator.estimateSmartFee(conf_target, &feeCalc, conservative)};
-    CFeeRate min_mempool_feerate{mempool.GetMinFee(gArgs.GetIntArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000)};
-    CFeeRate min_relay_feerate{::minRelayTxFee};
-    feeRate = std::max({feeRate, min_mempool_feerate, min_relay_feerate});
     if (feeRate != CFeeRate(0)) {
+        CFeeRate min_mempool_feerate{mempool.GetMinFee(gArgs.GetIntArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000)};
+        CFeeRate min_relay_feerate{::minRelayTxFee};
+        feeRate = std::max({feeRate, min_mempool_feerate, min_relay_feerate});
         result.pushKV("feerate", ValueFromAmount(feeRate.GetFeePerK()));
     } else {
         errors.push_back("Insufficient data or no feerate found");