Fix: Preserve relid and cdbpolicy in make_grouping_rel

make_grouping_rel() failed to set the relid and cdbpolicy fields
in the grouped_rel it constructs.  As a result, extensions using
create_upper_paths_hook could see uninitialized values and crash
when accessing these fields.

The fix is to propagate the values from input_rel, so that
grouped_rel carries the same relid and distribution policy as its
input.  This ensures that hooks and subsequent planner logic can
safely rely on them.

Author: yjhjstz

src/backend/optimizer/plan/planner.c

@@ -4263,6 +4263,8 @@ make_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel,
 	grouped_rel->useridiscurrent = input_rel->useridiscurrent;
 	grouped_rel->fdwroutine = input_rel->fdwroutine;
 	grouped_rel->exec_location = input_rel->exec_location;
+	grouped_rel->cdbpolicy = input_rel->cdbpolicy;
+	grouped_rel->relid = input_rel->relid;
 
 	return grouped_rel;
 }