pay: make sure we don't think payment in progress if it immediately fails.

If send_htlc_out() fails, it doesn't initialize pc->out; that can
make us think it's still in progress.

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

lightningd/pay.c

@@ -252,6 +252,7 @@ static void send_payment(struct command *cmd,
 	pc->ids = tal_steal(pc, ids);
 	pc->msatoshi = route[n_hops-1].amount;
 	pc->path_secrets = tal_steal(pc, path_secrets);
+	pc->out = NULL;
 
 	log_info(cmd->ld->log, "Sending %u over %zu hops to deliver %"PRIu64,
 		 route[0].amount, n_hops, pc->msatoshi);