`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 <amount.h>
#include <chain.h>
#include <consensus/validation.h>
#include <core_io.h>
#include <httpserver.h>
#include <init.h>
#include <interfaces/chain.h>
#include <validation.h>
#include <key_io.h>
#include <net.h>
#include <outputtype.h>
#include <policy/feerate.h>
#include <policy/fees.h>
#include <policy/policy.h>
#include <policy/rbf.h>
#include <rpc/mining.h>
#include <rpc/rawtransaction.h>
#include <rpc/server.h>
#include <rpc/util.h>
#include <script/sign.h>
#include <shutdown.h>
#include <timedata.h>
#include <util/system.h>
#include <util/moneystr.h>
#include <wallet/coincontrol.h>