[DO NOT MERGE] Fix associations serialization optimization bug

There mas a missing defensive copy causing false positive detections of
"associations not changed" case, leading to xml file not being updated once
at least one record is present

Bug: 30932767
Test: Associate at least two different devices and ensure the xml has both.
Change-Id: Ic0dc615dd2b847e137555c1084c616831b4dde83