BUG-650: speed up ResolveDataChangeState.needsProcessing()

Checking for empty subBuilders allows us to reuse the parent's
collection. For simple cases with no listeners whis speeds up
needsProcessing() by completely reusing the emptyList and for
non-trivial cases it just omits object instantiation.

Change-Id: Ib3089bca2ec4f7e1ef826bf4192b8154ff154702
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-650: speed up ResolveDataChangeState.needsProcessing()"