Simplify how to we handle background task expirations. (#3670)

ElementX/Sources/Application/AppCoordinator.swift

@@ -965,16 +965,14 @@ class AppCoordinator: AppCoordinatorProtocol, AuthenticationFlowCoordinatorDeleg
             return
         }
         
-        backgroundTask = appMediator.beginBackgroundTask { [weak self] in
+        backgroundTask = appMediator.beginBackgroundTask {
-            guard let self else { return }
-            
             MXLog.info("Background task is about to expire.")
-            stopSync(isBackgroundTask: true) { [weak self] in
-                guard let self, let backgroundTask else { return }
             
-                MXLog.info("Ending background task.")
+            // We're intentionally strongly retaining self here to an EXC_BAD_ACCESS
-                appMediator.endBackgroundTask(backgroundTask)
+            // `backgroundTask` will be eventually released in `endActiveBackgroundTask`
-                self.backgroundTask = nil
+            // https://sentry.tools.element.io/organizations/element/issues/4477794/events/9cfd04e4d045440f87498809cf718de5/
+            self.stopSync(isBackgroundTask: true) {
+                self.endActiveBackgroundTask()
             }
         }
     }
@@ -982,13 +980,18 @@ class AppCoordinator: AppCoordinatorProtocol, AuthenticationFlowCoordinatorDeleg
     @objc
     private func applicationDidBecomeActive() {
         MXLog.info("Application did become active")
+        endActiveBackgroundTask()
+        startSync()
+    }
     
-        if let backgroundTask {
+    private func endActiveBackgroundTask() {
-            appMediator.endBackgroundTask(backgroundTask)
+        guard let backgroundTask else {
-            self.backgroundTask = nil
+            return
         }
         
-        startSync()
+        MXLog.info("Ending background task.")
+        appMediator.endBackgroundTask(backgroundTask)
+        self.backgroundTask = nil
     }
     
     // MARK: Background app refresh