Fix Background Task Manager

* Removed `weak` reference to delegate as it was immediately null after being set in startup code
* Therefore, all calls to the delegate were falling through the guard statement

Author: nan-li

iOS_SDK/OneSignalSDK/OneSignalOSCore/Source/OSBackgroundTaskManager.swift

@@ -26,6 +26,7 @@
  */
 
 import Foundation
+import OneSignalCore
 
 @objc
 public protocol OSBackgroundTaskManagerDelegate {
@@ -39,12 +40,12 @@ public protocol OSBackgroundTaskManagerDelegate {
 // check if Core needs to use this, then ok to live here
 @objc
 public class OSBackgroundTaskManager: NSObject {
-    @objc public static weak var delegate: OSBackgroundTaskManagerDelegate?
+    @objc public static var delegate: OSBackgroundTaskManagerDelegate? // TODO: This used to be weak, is that still necessary
 
     @objc
     public static func beginBackgroundTask(_ taskIdentifier: String) {
         guard let delegate = delegate else {
-            // Log error, no delegate
+            OneSignalLog.onesignalLog(.LL_ERROR, message: "OSBackgroundTaskManager:beginBackgroundTask \(taskIdentifier) cannot be executed due to no delegate.")
             return
         }
         delegate.beginBackgroundTask(taskIdentifier)
@@ -53,7 +54,7 @@ public class OSBackgroundTaskManager: NSObject {
     @objc
     public static func endBackgroundTask(_ taskIdentifier: String) {
         guard let delegate = delegate else {
-            // Log error, no delegate
+            OneSignalLog.onesignalLog(.LL_ERROR, message: "OSBackgroundTaskManager:endBackgroundTask \(taskIdentifier) cannot be executed due to no delegate.")
             return
         }
         delegate.endBackgroundTask(taskIdentifier)
@@ -62,7 +63,7 @@ public class OSBackgroundTaskManager: NSObject {
     @objc
     public static func setTaskInvalid(_ taskIdentifier: String) {
         guard let delegate = delegate else {
-            // Log error, no delegate
+            OneSignalLog.onesignalLog(.LL_ERROR, message: "OSBackgroundTaskManager:setTaskInvalid \(taskIdentifier) cannot be executed due to no delegate.")
             // But not necessarily an error because this task won't exist
             // Can be called in initialization of services before delegate is set
             return