`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.
change_position = options["changePosition"].get_int();
        if (options.exists("change_type")) {
            if (options.exists("changeAddress")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both changeAddress and address_type options");
            }
            coinControl.m_change_type = pwallet->m_default_change_type;
            if (!ParseOutputType(options["change_type"].get_str(), *coinControl.m_change_type)) {
                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown change type '%s'", options["change_type"].get_str()));
            }
        }
        if (options.exists("includeWatching"))
            coinControl.fAllowWatchOnly = options["includeWatching"].get_bool();
        if (options.exists("lockUnspents"))
            lockUnspents = options["lockUnspents"].get_bool();
        if (options.exists("feeRate"))
        {
            coinControl.m_feerate = CFeeRate(AmountFromValue(options["feeRate"]));
            coinControl.fOverrideFeeRate = true;
        }
        if (options.exists("subtractFeeFromOutputs"))
            subtractFeeFromOutputs = options["subtractFeeFromOutputs"].get_array();
        if (options.exists("replaceable")) {
            coinControl.m_signal_bip125_rbf = options["replaceable"].get_bool();
        }
        if (options.exists("conf_target")) {
            if (options.exists("feeRate")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both conf_target and feeRate");
            }
            coinControl.m_confirm_target = ParseConfirmTarget(options["conf_target"]);
        }