`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.
{
    
    
    
    CBlockIndex* startBlock = nullptr;
    {
        auto locked_chain = chain().lock();
        startBlock = chainActive.FindEarliestAtLeast(startTime - TIMESTAMP_WINDOW);
        WalletLogPrintf("%s: Rescanning last %i blocks\n", __func__, startBlock ? chainActive.Height() - startBlock->nHeight + 1 : 0);
    }
    if (startBlock) {
        const CBlockIndex* failedBlock;
        
        if (ScanResult::FAILURE == ScanForWalletTransactions(startBlock, nullptr, reserver, failedBlock, update)) {
            return failedBlock->GetBlockTimeMax() + TIMESTAMP_WINDOW + 1;
        }
    }
    return startTime;
}
/**
 * Scan the block chain (starting in pindexStart) for transactions
 * from or to us. If fUpdate is true, found transactions that already
 * exist in the wallet will be updated.
 *
 * @param[in] pindexStop if not a nullptr, the scan will stop at this block-index
 * @param[out] failed_block if FAILURE is returned, will be set to the most
 *    recent block that could not be scanned, otherwise nullptr
 *
 * @return ScanResult indicating success or failure of the scan. SUCCESS if