6745 AndroidJNI.FindClass can return negative values

https://swrvedev.jira.com/browse/SWRVE-6745

When converting the pointer to the class it can result in a negative pointer. This was causing the SDK to not register for push notifications on Android.
would it be worth updating the [readme](https://github.com/Swrve/swrve-sdk/blob/release-3_3/README.md) as the `FindClass` method has historically been a source of errors?