fix apply on user-defined aggregate init (souffle-lang#2456)

The `init` expression of user-define aggregates was never
handed-over to `apply`'s `mapper`.

One visible issue is that the `TupleId` transformer would not update the
tuple of the `init` expression while shuffling tuple identifiers.
That would then result in the `init` expression peeking data in the
wrong tuple during execution of the RAM program.

src/ram/Aggregate.h

@@ -72,6 +72,7 @@ class Aggregate : public RelationOperation, public AbstractAggregate {
         for (auto &elem : orderBy) {
             elem->expr = map(std::move(elem->expr));
         }
+        function->apply(map);
     }
 
     static bool classof(const Node* n) {

src/ram/IndexAggregate.h

@@ -74,6 +74,7 @@ class IndexAggregate : public IndexOperation, public AbstractAggregate {
         for (auto &elem : orderBy) {
             elem->expr = map(std::move(elem->expr));
         }
+        function->apply(map);
     }
 
     static bool classof(const Node* n) {