lightningd: fix crash when we get onchain after old db.

lightningd(25923): lightning_onchaind(03cbf298b068300be33f06c947b9d3f00a0f0e8089da3233f5db37e81d3a596fe1): UPDATE WIRE_ONCHAIN_MISSING_HTLC_OUTPUT
lightningd(25923): FATAL SIGNAL 11 RECEIVED
lightningd(25923): backtrace: lightningd/log.c:498 (log_crash) 0x410ae8
lightningd(25923): backtrace: (null):0 ((null)) 0x7ff2ddb8e0df
lightningd(25923): backtrace: lightningd/pay.c:231 (local_routing_failure) 0x415b33
lightningd(25923): backtrace: lightningd/pay.c:383 (payment_failed) 0x41604c
lightningd(25923): backtrace: lightningd/peer_htlcs.c:783 (onchain_failed_our_htlc) 0x4225e5
lightningd(25923): backtrace: lightningd/peer_control.c:1209 (handle_missing_htlc_output) 0x41b31c
lightningd(25923): backtrace: lightningd/peer_control.c:1323 (onchain_msg) 0x41b759
lightningd(25923): backtrace: lightningd/subd.c:498 (sd_msg_read) 0x425b40

Fixes: #878
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/pay.c

@@ -382,6 +382,21 @@ void payment_failed(struct lightningd *ld, const struct htlc_out *hout,
 	payment = wallet_payment_by_hash(tmpctx, ld->wallet,
 					 &hout->payment_hash);
 
+	/* FIXME: Prior to 299b280f7, we didn't put route_nodes and
+	 * route_channels in db.  If this happens, it's an old payment,
+	 * so we can simply mark it failed in db and return. */
+	if (!payment->route_channels) {
+		log_unusual(hout->key.channel->log,
+			    "No route_channels for htlc %s:"
+			    " was this an old database?",
+			    type_to_string(ltmp, struct sha256,
+					   &hout->payment_hash));
+		wallet_payment_set_status(ld->wallet, &hout->payment_hash,
+					  PAYMENT_FAILED, NULL);
+		tal_free(tmpctx);
+		return;
+	}
+
 	/* This gives more details than a generic failure message */
 	if (localfail) {
 		fail = local_routing_failure(tmpctx, ld, hout, payment);