Handle IndexedDb errors in unsubscribe callback

Addresses one of the three problems I found during randomized testing.

Author: schmidt-sebastian

packages/firestore/src/core/event_manager.ts

@@ -102,21 +102,19 @@ export class EventManager implements SyncEngineListener {
 
   async unlisten(listener: QueryListener): Promise<void> {
     const query = listener.query;
-    let lastListen = false;
 
     const queryInfo = this.queries.get(query);
     if (queryInfo) {
       const i = queryInfo.listeners.indexOf(listener);
       if (i >= 0) {
-        queryInfo.listeners.splice(i, 1);
-        lastListen = queryInfo.listeners.length === 0;
+        if (queryInfo.listeners.length > 1) {
+          queryInfo.listeners.splice(i, 1);
+        } else {
+          await this.syncEngine.unlisten(query);
+          this.queries.delete(query);
+        }
       }
     }
-
-    if (lastListen) {
-      this.queries.delete(query);
-      return this.syncEngine.unlisten(query);
-    }
   }
 
   onWatchChange(viewSnaps: ViewSnapshot[]): void {

packages/firestore/src/core/firestore_client.ts

@@ -404,7 +404,7 @@ export class FirestoreClient {
     if (this.clientTerminated) {
       return;
     }
-    this.asyncQueue.enqueueAndForget(() => {
+    this.asyncQueue.enqueueRetryable(() => {
       return this.eventMgr.unlisten(listener);
     });
   }