`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::vector<std::string> GetDestValues(const std::string& prefix) const;
    
    bool AddWatchOnly(const CScript& dest, int64_t nCreateTime) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    bool RemoveWatchOnly(const CScript &dest) override EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    
    bool LoadWatchOnly(const CScript &dest);
    
    int64_t nRelockTime = 0;
    bool Unlock(const SecureString& strWalletPassphrase);
    bool ChangeWalletPassphrase(const SecureString& strOldWalletPassphrase, const SecureString& strNewWalletPassphrase);
    bool EncryptWallet(const SecureString& strWalletPassphrase);
    void GetKeyBirthTimes(interfaces::Chain::Lock& locked_chain, std::map<CTxDestination, int64_t> &mapKeyBirth) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    unsigned int ComputeTimeSmart(const CWalletTx& wtx) const;
    /**
     * Increment the next transaction order id
     * @return next transaction order id
     */
    int64_t IncOrderPosNext(WalletBatch *batch = nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    DBErrors ReorderTransactions();
    void MarkDirty();
    bool AddToWallet(const CWalletTx& wtxIn, bool fFlushOnClose=true);
    void LoadToWallet(const CWalletTx& wtxIn) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    void TransactionAddedToMempool(const CTransactionRef& tx) override;
    void BlockConnected(const std::shared_ptr<const CBlock>& pblock, const CBlockIndex *pindex, const std::vector<CTransactionRef>& vtxConflicted) override;
    void BlockDisconnected(const std::shared_ptr<const CBlock>& pblock) override;
    int64_t RescanFromTime(int64_t startTime, const WalletRescanReserver& reserver, bool update);
    enum class ScanResult {
        SUCCESS,
        FAILURE,
        USER_ABORT