Report memory context stats upon out-of-memory in repalloc[_huge].

This longstanding functionality evidently got lost in commit
3d6d1b58.  Noted while studying an OOM report from Jaime
Casanova.  Backpatch to 9.5 where the bug was introduced.

src/backend/utils/mmgr/mcxt.c

@@ -1051,10 +1051,13 @@ repalloc(void *pointer, Size size)
 
 	ret = (*context->methods->realloc) (context, pointer, size);
 	if (ret == NULL)
+	{
+		MemoryContextStats(TopMemoryContext);
 		ereport(ERROR,
 				(errcode(ERRCODE_OUT_OF_MEMORY),
 				 errmsg("out of memory"),
 				 errdetail("Failed on request of size %zu.", size)));
+	}
 
 	VALGRIND_MEMPOOL_CHANGE(context, pointer, ret, size);
 
@@ -1131,10 +1134,13 @@ repalloc_huge(void *pointer, Size size)
 
 	ret = (*context->methods->realloc) (context, pointer, size);
 	if (ret == NULL)
+	{
+		MemoryContextStats(TopMemoryContext);
 		ereport(ERROR,
 				(errcode(ERRCODE_OUT_OF_MEMORY),
 				 errmsg("out of memory"),
 				 errdetail("Failed on request of size %zu.", size)));
+	}
 
 	VALGRIND_MEMPOOL_CHANGE(context, pointer, ret, size);