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 (current_fee < 0) {
        return util::Error{Untranslated(STR_INTERNAL_BUG("Fee paid < 0"))};
    }
    
    if (nChangePosInOut != -1 && fee_needed < current_fee) {
        auto& change = txNew.vout.at(nChangePosInOut);
        change.nValue += current_fee - fee_needed;
        current_fee = result.GetSelectedValue() - CalculateOutputValue(txNew);
        if (fee_needed != current_fee) {
            return util::Error{Untranslated(STR_INTERNAL_BUG("Change adjustment: Fee needed != fee paid"))};
        }
    }
    
    if (coin_selection_params.m_subtract_fee_outputs) {
        CAmount to_reduce = fee_needed - current_fee;
        int i = 0;
        bool fFirst = true;
        for (const auto& recipient : vecSend)
        {
            if (i == nChangePosInOut) {
                ++i;
            }
            CTxOut& txout = txNew.vout[i];
            if (recipient.fSubtractFeeFromAmount)
            {
                txout.nValue -= to_reduce / outputs_to_subtract_fee_from; 
                if (fFirst) 
                {
                    fFirst = false;
                    txout.nValue -= to_reduce % outputs_to_subtract_fee_from;