Have this warning while building current master (0bd4929cd00e91bf4137f43b097cd62f72f503e4) on one test machine.
```
wallet/rpcwallet.cpp: In function 'rescanblockchain()::<lambda(const RPCHelpMan&, const JSONRPCRequest&)>':
wallet/rpcwallet.cpp:3596:19: warning: '*((void*)& stop_height +4)' may be used uninitialized in this function [-Wmaybe-uninitialized]
 3596 |     Optional<int> stop_height;
      |                   ^~~~~~~~~~~
```
```
$ gcc --version
gcc (Gentoo 9.2.0-r2 p3) 9.2.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ uname -a
Linux red-box 4.19.72-gentoo #2 SMP Sun Sep 22 03:00:01 EEST 2019 x86_64 Intel(R) Pentium(R) CPU N3710 @ 1.60GHz GenuineIntel GNU/Linux
```
if (!wallet) return NullUniValue;
    CWallet* const pwallet = wallet.get();
    std::string flag_str = request.params[0].get_str();
    bool value = request.params[1].isNull() || request.params[1].get_bool();
    if (!WALLET_FLAG_MAP.count(flag_str)) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Unknown wallet flag: %s", flag_str));
    }
    auto flag = WALLET_FLAG_MAP.at(flag_str);
    if (!(flag & MUTABLE_WALLET_FLAGS)) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Wallet flag is immutable: %s", flag_str));
    }
    UniValue res(UniValue::VOBJ);
    if (pwallet->IsWalletFlagSet(flag) == value) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Wallet flag is already set to %s: %s", value ? "true" : "false", flag_str));
    }
    res.pushKV("flag_name", flag_str);
    res.pushKV("flag_state", value);
    if (value) {
        pwallet->SetWalletFlag(flag);
    } else {
        pwallet->UnsetWalletFlag(flag);
    }
    if (flag && value && WALLET_FLAG_CAVEATS.count(flag)) {
        res.pushKV("warnings", WALLET_FLAG_CAVEATS.at(flag));
    }
    return res;
},
    };
}
static RPCHelpMan createwallet()