`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.
class CNode;
struct CConnmanTest {
    static void AddNode(CNode& node);
    static void ClearNodes();
};
class PeerLogicValidation;
struct TestingSetup: public BasicTestingSetup {
    boost::thread_group threadGroup;
    CConnman* connman;
    CScheduler scheduler;
    std::unique_ptr<PeerLogicValidation> peerLogic;
    explicit TestingSetup(const std::string& chainName = CBaseChainParams::MAIN);
    ~TestingSetup();
};
class CBlock;
struct CMutableTransaction;
class CScript;
struct TestChain100Setup : public TestingSetup {
    TestChain100Setup();
    
    
    CBlock CreateAndProcessBlock(const std::vector<CMutableTransaction>& txns,
                                 const CScript& scriptPubKey);
    ~TestChain100Setup();
    std::vector<CTransactionRef> m_coinbase_txns; 
    CKey coinbaseKey; 
};
class CTxMemPoolEntry;