Use -1 as the default lastResponseTime

Entites that didn't have an updatedAt time at the time of creation will
default to having one set to 0.  Since entities with an updatedAt time
greater than lastResponseTime is expected to be returned this means that
these entities would not be included when a client does its initial sync
subscribing to a resource.  Change the default lastResponseTime
requested so that these entities are included.

packages/lib/src/subscriptions.ts

@@ -208,7 +208,7 @@ export class SubscriptionController {
 export class EventSubscriber<T extends Event<T>, V=T> {
 	_callbacks = new Array<EventSubscriberCallback<V>>();
 	lastResponse: Event<T> | null = null;
-	lastResponseTime = 0;
+	lastResponseTime = -1;
 	control?: Link;
 
 	constructor(

test/lib/subscriptions.js

@@ -63,8 +63,8 @@ describe("lib/subscriptions", function() {
 			assert.deepEqual(reconstructed, response);
 		});
 
-		it("should be round trip json serialisable with a null event replay", function() {
-			const response = new lib.SubscriptionResponse(null);
+		it("should be round trip json serialisable with an undefined event replay", function() {
+			const response = new lib.SubscriptionResponse(undefined);
 			const json = JSON.stringify(response);
 			assert.equal(typeof json, "string");
 			const reconstructed = lib.SubscriptionResponse.fromJSON(JSON.parse(json));
@@ -396,13 +396,13 @@ describe("lib/subscriptions", function() {
 
 		describe("_updateSubscription()", function() {
 			it("should correctly request a subscription", async function() {
-				const expected = new lib.SubscriptionRequest(RegisteredEvent.name, true);
+				const expected = new lib.SubscriptionRequest(RegisteredEvent.name, true, -1);
 				registeredEvent.subscribe(() => true);
 				await events.once(mockControl.connector, "send");
 				assertLastRequest(expected);
 			});
-			it("should correctly request a no subscriptions", async function() {
-				const expected = new lib.SubscriptionRequest(RegisteredEvent.name, false);
+			it("should correctly request no subscriptions", async function() {
+				const expected = new lib.SubscriptionRequest(RegisteredEvent.name, false, -1);
 				function callback() {}
 				registeredEvent.subscribe(callback);
 				await events.once(mockControl.connector, "send");