[fuzz] Show that SRD budgets for non-dust change

Adding this assert to the fuzz test without increasing the change target
by the change_fee resulted in a crash within a few seconds.

Author: murchandamus

src/wallet/test/fuzz/coinselection.cpp

@@ -91,7 +91,10 @@ FUZZ_TARGET(coinselection)
     const auto result_bnb = SelectCoinsBnB(group_pos, target, cost_of_change, MAX_STANDARD_TX_WEIGHT);
 
     auto result_srd = SelectCoinsSRD(group_pos, target, coin_params.m_change_fee, fast_random_context, MAX_STANDARD_TX_WEIGHT);
-    if (result_srd) result_srd->ComputeAndSetWaste(cost_of_change, cost_of_change, 0);
+    if (result_srd) {
+        assert(result_srd->GetChange(CHANGE_LOWER, coin_params.m_change_fee) > 0); // Demonstrate that SRD creates change of at least CHANGE_LOWER
+        result_srd->ComputeAndSetWaste(cost_of_change, cost_of_change, 0);
+    }
 
     CAmount change_target{GenerateChangeTarget(target, coin_params.m_change_fee, fast_random_context)};
     auto result_knapsack = KnapsackSolver(group_all, target, change_target, fast_random_context, MAX_STANDARD_TX_WEIGHT);