`ScanForWalletTransactions()` has the following comment about its return value:

```
 * Returns null if scan was successful. Otherwise, if a complete rescan was not
 * possible (due to pruning or corruption), returns pointer to the most recent
 * block that could not be scanned.
```

This is not strictly true. If `abortrescan` is called, then `ScanForWalletTransactions()` will return `nullptr`, even though the scan wasn't successful to the tip.

This in turn causes a minor bug in `importmulti`, where the call doesn't return the correct error and warning about potentially not finding transactions if `abortrescan` was called.

I think the correct fix is for `ScanForWalletTransactions()` to inform the caller that the rescan was aborted.
std::set<int> setSubtractFeeFromOutputs;
    if (!options.isNull()) {
      if (options.type() == UniValue::VBOOL) {
        
        coinControl.fAllowWatchOnly = options.get_bool();
      }
      else {
        RPCTypeCheckArgument(options, UniValue::VOBJ);
        RPCTypeCheckObj(options,
            {
                {"changeAddress", UniValueType(UniValue::VSTR)},
                {"changePosition", UniValueType(UniValue::VNUM)},
                {"change_type", UniValueType(UniValue::VSTR)},
                {"includeWatching", UniValueType(UniValue::VBOOL)},
                {"lockUnspents", UniValueType(UniValue::VBOOL)},
                {"feeRate", UniValueType()}, 
                {"subtractFeeFromOutputs", UniValueType(UniValue::VARR)},
                {"replaceable", UniValueType(UniValue::VBOOL)},
                {"conf_target", UniValueType(UniValue::VNUM)},
                {"estimate_mode", UniValueType(UniValue::VSTR)},
            },
            true, true);
        if (options.exists("changeAddress")) {
            CTxDestination dest = DecodeDestination(options["changeAddress"].get_str());
            if (!IsValidDestination(dest)) {
                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "changeAddress must be a valid bitcoin address");
            }
            coinControl.destChange = dest;
        }
        if (options.exists("changePosition"))