wallet: compute waste for SelectionResults of preset inputs

When we use only manually specified inputs, we should still calculate
the waste so that if anything later on calls GetWaste (in order to log
it), there won't be an error.

src/wallet/spend.cpp

@@ -438,6 +438,7 @@ std::optional<SelectionResult> SelectCoins(const CWallet& wallet, const std::vec
         SelectionResult result(nTargetValue, SelectionAlgorithm::MANUAL);
         result.AddInput(preset_inputs);
         if (result.GetSelectedValue() < nTargetValue) return std::nullopt;
+        result.ComputeAndSetWaste(coin_selection_params.m_cost_of_change);
         return result;
     }
 
@@ -573,6 +574,9 @@ std::optional<SelectionResult> SelectCoins(const CWallet& wallet, const std::vec
 
     // Add preset inputs to result
     res->AddInput(preset_inputs);
+    if (res->m_algo == SelectionAlgorithm::MANUAL) {
+        res->ComputeAndSetWaste(coin_selection_params.m_cost_of_change);
+    }
 
     return res;
 }