Make sure to actually return after jniThrowException

It's illegal to keep using JNIEnv with a pending
exception, and also a bit nonsensical to keep doing work
if it's just going to throw when the native method returns

Change-Id: I6ce66fc0d00f05a6fc33202c4aef266860472701
Fixes: 124064285
Test: android.graphics.cts.EGL15Test CTS test