When importing a watch-only address over `importmulti` with a specific timestamp, the wallet's `nTimeFirstKey` will be set to 1.
I think we should add a optional timestamp to `CWallet::AddWatchOnly()` and use it when importing addresses or pubkeys.

LogPrintf("AddToWallet(): found %s in block %s not in index\n",
                         wtxIn.GetHash().ToString(),
                         wtxIn.hashBlock.ToString());
        }
        AddToSpends(hash);
    }
    bool fUpdated = false;
    if (!fInsertedNew)
    {
        
        if (!wtxIn.hashUnset() && wtxIn.hashBlock != wtx.hashBlock)
        {
            wtx.hashBlock = wtxIn.hashBlock;
            fUpdated = true;
        }
        
        if (wtxIn.hashBlock.IsNull() && wtx.isAbandoned())
        {
            wtx.hashBlock = wtxIn.hashBlock;
            fUpdated = true;
        }
        if (wtxIn.nIndex != -1 && (wtxIn.nIndex != wtx.nIndex))
        {
            wtx.nIndex = wtxIn.nIndex;
            fUpdated = true;
        }
        if (wtxIn.fFromMe && wtxIn.fFromMe != wtx.fFromMe)
        {
            wtx.fFromMe = wtxIn.fFromMe;
            fUpdated = true;