`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.
struct TestMemPoolEntryHelper
{
    
    CAmount nFee;
    int64_t nTime;
    unsigned int nHeight;
    bool spendsCoinbase;
    unsigned int sigOpCost;
    LockPoints lp;
    TestMemPoolEntryHelper() :
        nFee(0), nTime(0), nHeight(1),
        spendsCoinbase(false), sigOpCost(4) { }
    CTxMemPoolEntry FromTx(const CMutableTransaction& tx);
    CTxMemPoolEntry FromTx(const CTransactionRef& tx);
    
    TestMemPoolEntryHelper &Fee(CAmount _fee) { nFee = _fee; return *this; }
    TestMemPoolEntryHelper &Time(int64_t _time) { nTime = _time; return *this; }
    TestMemPoolEntryHelper &Height(unsigned int _height) { nHeight = _height; return *this; }
    TestMemPoolEntryHelper &SpendsCoinbase(bool _flag) { spendsCoinbase = _flag; return *this; }
    TestMemPoolEntryHelper &SigOpsCost(unsigned int _sigopsCost) { sigOpCost = _sigopsCost; return *this; }
};
CBlock getBlock13b8a();
std::ostream& operator<<(std::ostream& os, const uint256& num);
#endif