`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 CCoinControl;
class COutput;
class CReserveKey;
class CScript;
class CTxMemPool;
class CBlockPolicyEstimator;
class CWalletTx;
struct FeeCalculation;
enum class FeeEstimateMode;
enum WalletFeature
{
    FEATURE_BASE = 10500, 
    FEATURE_WALLETCRYPT = 40000, 
    FEATURE_COMPRPUBKEY = 60000, 
    FEATURE_HD = 130000, 
    FEATURE_HD_SPLIT = 139900, 
    FEATURE_NO_DEFAULT_KEY = 159900, 
    FEATURE_PRE_SPLIT_KEYPOOL = 169900, 
    FEATURE_LATEST = FEATURE_PRE_SPLIT_KEYPOOL
};
constexpr OutputType DEFAULT_ADDRESS_TYPE{OutputType::P2SH_SEGWIT};
constexpr OutputType DEFAULT_CHANGE_TYPE{OutputType::CHANGE_AUTO};
enum WalletFlags : uint64_t {