Fixes the fix of wrong completionHandler call

Unfortunately the last fix introduces a new bug! The call for `[[UIApplication sharedApplication] registerForRemoteNotifications]` *must* be handled on main thread! This is fixed now.

permission_handler/ios/Classes/strategies/NotificationPermissionStrategy.m

@@ -38,8 +38,10 @@
           return;
           return;
         }
         }
 
 
-        [[UIApplication sharedApplication] registerForRemoteNotifications];
-        completionHandler(PermissionStatusGranted);
+        dispatch_async(dispatch_get_main_queue(), ^{
+            [[UIApplication sharedApplication] registerForRemoteNotifications];
+            completionHandler(PermissionStatusGranted);
+        });
       }];
       }];
 
 
     } else {
     } else {