A user reported to me that they are unable to create a PSBT with a legacy watchonly wallet when they use the GUI. They get an error "The amount exceeds your balance".

I think the issue is that the GUI will retrieve the wallet's balance via `AvailableCoins` before calling `CreateTransaction`. This call to `AvailableCoins` is resulting in fewer coins being returned with recent changes to how `AvailableCoins` works, particularly with additional filtering of spendable coins and preset coins.

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Note that this does not effect descriptor wallets. A workaround for this issue is to switch to using descriptor wallets. An existing legacy wallet can be turned into a descriptor wallet using the `migratewallet` RPC. However many watchonly legacy wallets are likely the result of importing descriptors via `importmulti`. For such wallets, I recommend creating a new descriptor wallet and re-importing the descriptors.
if (index+1 > static_cast<int>(confTargets.size())) {
        return confTargets.back();
    }
    if (index < 0) {
        return confTargets[0];
    }
    return confTargets[index];
}
int getIndexForConfTarget(int target) {
    for (unsigned int i = 0; i < confTargets.size(); i++) {
        if (confTargets[i] >= target) {
            return i;
        }
    }
    return confTargets.size() - 1;
}
SendCoinsDialog::SendCoinsDialog(const PlatformStyle *_platformStyle, QWidget *parent) :
    QDialog(parent, GUIUtil::dialog_flags),
    ui(new Ui::SendCoinsDialog),
    m_coin_control(new CCoinControl),
    platformStyle(_platformStyle)
{
    ui->setupUi(this);
    if (!_platformStyle->getImagesOnButtons()) {
        ui->addButton->setIcon(QIcon());
        ui->clearButton->setIcon(QIcon());
        ui->sendButton->setIcon(QIcon());
    } else {
        ui->addButton->setIcon(_platformStyle->SingleColorIcon(":/icons/add"));
        ui->clearButton->setIcon(_platformStyle->SingleColorIcon(":/icons/remove"));