fixup! lightningd: Add signinvoice to sign a BOLT11 invoice.

Don't require expiry (the default is 1 hour), and allow
description-hash-only invoices.  Use a BOLT quote.

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

lightningd/invoice.c

@@ -1840,14 +1840,14 @@ static struct command_result *json_signinvoice(struct command *cmd,
 	char *b11enc = bolt11_encode(cmd, b11, have_n,
 				     hsm_sign_b11, cmd->ld);
 
-	if (!b11->description)
+	/* BOLT #11:
+	 * A writer:
+	 *   - MUST include either exactly one `d` or exactly one `h` field.
+	 */
+	if (!b11->description && !b11->description_hash)
 		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
 				    "Missing description in invoice");
 
-	if (!b11->expiry)
-		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
-				    "Missing expiry in invoice");
-
 	response = json_stream_success(cmd);
 	json_add_invstring(response, b11enc);
 	return command_success(cmd, response);