Short-circuit room list store dispatch handling if not ready

We were taking 0.2ms to handle the registration of a timer per event during startup, even before the app is visible to the user. These timers would be short-circuited too, leading to a bunch of wasted time.

0.2ms isn't a lot of time, but multiplied by thousands of events at startup it's pretty significant.

On my account this reduces the full page spinner time from ~50 seconds to just over 20 seconds.

src/stores/room-list/RoomListStore.ts

@@ -168,6 +168,12 @@ export class RoomListStoreClass extends AsyncStoreWithClient<IState> {
     }
 
     protected async onAction(payload: ActionPayload) {
+        // If we're not remotely ready, don't even bother scheduling the dispatch handling.
+        // This is repeated in the handler just in case things change between a decision here and
+        // when the timer fires.
+        const logicallyReady = this.matrixClient && this.initialListsGenerated;
+        if (!logicallyReady) return;
+
         // When we're running tests we can't reliably use setImmediate out of timing concerns.
         // As such, we use a more synchronous model.
         if (RoomListStoreClass.TEST_MODE) {