Avoid unecessary MemSet call (src/backend/utils/cache/relcache.c)

Hi hackers,

At function load_relcache_init_file, there is an unnecessary function call,
to initialize pgstat_info pointer to NULL.

MemSet(&rel->pgstat_info, 0, sizeof(rel->pgstat_info));

I think that intention with use of MemSet was:
MemSet(&rel->pgstat_info, 0, sizeof(*rel->pgstat_info));

Initialize with sizeof of Struct size, not with sizeof pointer size.
But so it breaks.

Attached a tiny patch.

regards,
Ranier Vilela