Don't store empty objects on SF traces

Proto3 doesn't store default values for object, however, it stored the
object start-end tags if an empty object was created.

Do not create objects when they are empty

Test: Flash a device. Record SF trace. Open them in the new winscope
version with "display defaults" unchecked. Check if there are no empty
objects

Change-Id: I3f48047e43e9c62c572d5b83e63a0f96527ef146