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
```
std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
    if (!wallet) return NullUniValue;
    CWallet* const pwallet = wallet.get();
    WalletRescanReserver reserver(*pwallet);
    if (!reserver.reserve()) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
    }
    int start_height = 0;
    Optional<int> stop_height;
    uint256 start_block;
    {
        LOCK(pwallet->cs_wallet);
        int tip_height = pwallet->GetLastBlockHeight();
        if (!request.params[0].isNull()) {
            start_height = request.params[0].get_int();
            if (start_height < 0 || start_height > tip_height) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid start_height");
            }
        }
        if (!request.params[1].isNull()) {
            stop_height = request.params[1].get_int();
            if (*stop_height < 0 || *stop_height > tip_height) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid stop_height");
            } else if (*stop_height < start_height) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "stop_height must be greater than start_height");
            }
        }
        
        if (!pwallet->chain().hasBlocks(pwallet->GetLastBlockHash(), start_height, stop_height)) {
            throw JSONRPCError(RPC_MISC_ERROR, "Can't rescan beyond pruned data. Use RPC call getblockchaininfo to determine your pruned height.");