`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.
#include <qt/test/wallettests.h>
#include <qt/test/util.h>
#include <interfaces/chain.h>
#include <interfaces/node.h>
#include <base58.h>
#include <qt/bitcoinamountfield.h>
#include <qt/optionsmodel.h>
#include <qt/platformstyle.h>
#include <qt/qvalidatedlineedit.h>
#include <qt/sendcoinsdialog.h>
#include <qt/sendcoinsentry.h>
#include <qt/transactiontablemodel.h>
#include <qt/transactionview.h>
#include <qt/walletmodel.h>
#include <key_io.h>
#include <test/test_bitcoin.h>
#include <validation.h>
#include <wallet/wallet.h>
#include <qt/overviewpage.h>
#include <qt/receivecoinsdialog.h>