Use safe string copy routine

Using memcpy with strlen as the size parameter will not take the
NULL terminator into account, relying instead on the destination
buffer being properly initialized. Replace with strlcpy which is
a safer alternative, and more in line with how we handle copying
strings elsewhere.

Author: Ranier Vilela <ranier.vf@gmail.com>
Discussion: https://postgr.es/m/CAEudQApAsbLsQ+gGiw-hT+JwGhgogFa_=5NUkgFO6kOPxyNidQ@mail.gmail.com

Author: danielgustafsson

src/backend/access/transam/xlog.c

@@ -8744,7 +8744,7 @@ do_pg_backup_start(const char *backupidstr, bool fast, List **tablespaces,
 				 errmsg("backup label too long (max %d bytes)",
 						MAXPGPATH)));
 
-	memcpy(state->name, backupidstr, strlen(backupidstr));
+	strlcpy(state->name, backupidstr, sizeof(state->name));
 
 	/*
 	 * Mark backup active in shared memory.  We must do full-page WAL writes