`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.
WALLET_FLAG_DISABLE_PRIVATE_KEYS = (1ULL << 32),
};
static constexpr uint64_t g_known_wallet_flags = WALLET_FLAG_DISABLE_PRIVATE_KEYS;
class CKeyPool
{
public:
    int64_t nTime;
    CPubKey vchPubKey;
    bool fInternal; 
    bool m_pre_split; 
    CKeyPool();
    CKeyPool(const CPubKey& vchPubKeyIn, bool internalIn);
    ADD_SERIALIZE_METHODS;
    template <typename Stream, typename Operation>
    inline void SerializationOp(Stream& s, Operation ser_action) {