A category to avoid background task leak
Drag the UIApplication + MPIBackgroundTaskProtection category files into the your project.
In my application, some SDKs don’t use the background task correctly, which caused a leak and was killed by the watchdog.
This category hooks three methods beginBackgroundTaskWithName, 
beginBackgroundTaskWithExpirationHandler:, and endBackgroundTask: to ensure that the endBackgroundTask: method is called.