`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 (!mapValue.count("n"))
    {
        nOrderPos = -1; 
        return;
    }
    nOrderPos = atoi64(mapValue["n"].c_str());
}
static inline void WriteOrderPos(const int64_t& nOrderPos, mapValue_t& mapValue)
{
    if (nOrderPos == -1)
        return;
    mapValue["n"] = i64tostr(nOrderPos);
}
struct COutputEntry
{
    CTxDestination destination;
    CAmount amount;
    int vout;
};
class CMerkleTx