`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::shared_ptr<CReserveKey> rKey = std::make_shared<CReserveKey>(this);
    CPubKey pubkey;
    if (!rKey->GetReservedKey(pubkey))
        return;
    script = rKey;
    script->reserveScript = CScript() << ToByteVector(pubkey) << OP_CHECKSIG;
}
void CWallet::LockCoin(const COutPoint& output)
{
    AssertLockHeld(cs_wallet); 
    setLockedCoins.insert(output);
}
void CWallet::UnlockCoin(const COutPoint& output)
{
    AssertLockHeld(cs_wallet); 
    setLockedCoins.erase(output);
}
void CWallet::UnlockAllCoins()
{
    AssertLockHeld(cs_wallet); 
    setLockedCoins.clear();
}
bool CWallet::IsLockedCoin(uint256 hash, unsigned int n) const
{
    AssertLockHeld(cs_wallet); 
    COutPoint outpt(hash, n);
    return (setLockedCoins.count(outpt) > 0);
}
void CWallet::ListLockedCoins(std::vector<COutPoint>& vOutpts) const