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.
{
    
    std::vector<SelectionResult> results;
    if (auto bnb_result{SelectCoinsBnB(groups.positive_group, nTargetValue, coin_selection_params.m_cost_of_change)}) {
        results.push_back(*bnb_result);
    }
    
    if (auto knapsack_result{KnapsackSolver(groups.mixed_group, nTargetValue, coin_selection_params.m_min_change_target, coin_selection_params.rng_fast)}) {
        knapsack_result->ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
        results.push_back(*knapsack_result);
    }
    if (auto srd_result{SelectCoinsSRD(groups.positive_group, nTargetValue, coin_selection_params.rng_fast)}) {
        srd_result->ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);