wallet: accurate SelectionResult::m_target

SelectionResult::m_target should be equal to actual selection target.
Selection target is the sum of all recipient amounts plus non input fees.
So we need to remove change_fee from the m_target. It's safe because change
target is always greater than the change fee, so we can always cover fees
if change output is created.

src/wallet/coinselection.cpp

@@ -166,6 +166,12 @@ std::optional<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& ut
 {
     SelectionResult result(target_value, SelectionAlgorithm::SRD);
 
+    // Include change for SRD as we want to avoid making really small change if the selection just
+    // barely meets the target. Just use the lower bound change target instead of the randomly
+    // generated one, since SRD will result in a random change amount anyway; avoid making the
+    // target needlessly large.
+    target_value += CHANGE_LOWER;
+
     std::vector<size_t> indexes;
     indexes.resize(utxo_pool.size());
     std::iota(indexes.begin(), indexes.end(), 0);