wallet: Use GetSelectionAmount for target value calculations

For target value calculations, GetSelectionAmount should be used, not
m_effective_value or m_value.

Specifically, ApproximateBestSubset mistakenly uses m_value when
calculating whether the target value has been met. This has been changed
to use GetSelectionAmount.

src/wallet/coinselection.cpp

@@ -195,7 +195,7 @@ static void ApproximateBestSubset(const std::vector<OutputGroup>& groups, const
                 //the selection random.
                 if (nPass == 0 ? insecure_rand.randbool() : !vfIncluded[i])
                 {
-                    nTotal += groups[i].m_value;
+                    nTotal += groups[i].GetSelectionAmount();
                     vfIncluded[i] = true;
                     if (nTotal >= nTargetValue)
                     {
@@ -205,7 +205,7 @@ static void ApproximateBestSubset(const std::vector<OutputGroup>& groups, const
                             nBest = nTotal;
                             vfBest = vfIncluded;
                         }
-                        nTotal -= groups[i].m_value;
+                        nTotal -= groups[i].GetSelectionAmount();
                         vfIncluded[i] = false;
                     }
                 }