`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.
if (!AddToWalletIfInvolvingMe(ptx, pindex, posInBlock, update_tx))
        return; 
    
    
    
    MarkInputsDirty(ptx);
}
void CWallet::TransactionAddedToMempool(const CTransactionRef& ptx) {
    auto locked_chain = chain().lock();
    LOCK(cs_wallet);
    SyncTransaction(ptx);
    auto it = mapWallet.find(ptx->GetHash());
    if (it != mapWallet.end()) {
        it->second.fInMempool = true;
    }
}
void CWallet::TransactionRemovedFromMempool(const CTransactionRef &ptx) {