ServiceType not checked in ServiceCollection

[AdityaRayamajhi]

Hello, Thanks for the brilliant work on OpenNetCf. However, In android we are getting crash issues once the application is hit back, running on the background and then resume it crashes. The issue is - it tries to Register and Add the Services again. I know it can be solved on the App level itself but I guess it would be better if it's been checked on the Service layer, on ServiceCollection before adding or registering serviceType. Thanks.