[rpc] throw JSONRPCError when utxo set can not be read

Github-Pull: #8832
Rebased-From: fa05cfdf25

src/rpc/blockchain.cpp

@@ -704,6 +704,8 @@ UniValue gettxoutsetinfo(const UniValue& params, bool fHelp)
         ret.push_back(Pair("bytes_serialized", (int64_t)stats.nSerializedSize));
         ret.push_back(Pair("hash_serialized", stats.hashSerialized.GetHex()));
         ret.push_back(Pair("total_amount", ValueFromAmount(stats.nTotalAmount)));
+    } else {
+        throw JSONRPCError(RPC_INTERNAL_ERROR, "Unable to read UTXO set");
     }
     return ret;
 }