Use NULL instead of 0 for pointer arguments.

Commit 5fe08c0 fixed this for calls to dshash_create().  This
commit fixes calls to dshash_attach() and dsa_create_in_place().

Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/aECi_gSD9JnVWQ8T%40nathan

Author: nathan-bossart

src/backend/replication/logical/launcher.c

@@ -1016,7 +1016,7 @@ logicalrep_launcher_attach_dshmem(void)
 		last_start_times_dsa = dsa_attach(LogicalRepCtx->last_start_dsa);
 		dsa_pin_mapping(last_start_times_dsa);
 		last_start_times = dshash_attach(last_start_times_dsa, &dsh_params,
-										 LogicalRepCtx->last_start_dsh, 0);
+										 LogicalRepCtx->last_start_dsh, NULL);
 	}
 
 	MemoryContextSwitchTo(oldcontext);

src/backend/utils/activity/pgstat_shmem.c

@@ -183,7 +183,7 @@ StatsShmemInit(void)
 		p += MAXALIGN(pgstat_dsa_init_size());
 		dsa = dsa_create_in_place(ctl->raw_dsa_area,
 								  pgstat_dsa_init_size(),
-								  LWTRANCHE_PGSTATS_DSA, 0);
+								  LWTRANCHE_PGSTATS_DSA, NULL);
 		dsa_pin(dsa);
 
 		/*
@@ -255,7 +255,8 @@ pgstat_attach_shmem(void)
 	dsa_pin_mapping(pgStatLocal.dsa);
 
 	pgStatLocal.shared_hash = dshash_attach(pgStatLocal.dsa, &dsh_params,
-											pgStatLocal.shmem->hash_handle, 0);
+											pgStatLocal.shmem->hash_handle,
+											NULL);
 
 	MemoryContextSwitchTo(oldcontext);
 }