lightningd: remember --log-file arg.

And fclose old ones if we get handed it multiple times.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/lightningd.c

@@ -56,6 +56,7 @@ static struct lightningd *new_lightningd(const tal_t *ctx,
 	htlc_out_map_init(&ld->htlcs_out);
 	ld->log_book = log_book;
 	ld->log = new_log(log_book, log_book, "lightningd(%u):", (int)getpid());
+	ld->logfile = NULL;
 	ld->alias = NULL;
 	ld->rgb = NULL;
 	list_head_init(&ld->connects);