Avoid resetting InCallAdapter when set.

This causes issues, for instance, when we have a MO and MT call ongoing. The associated users for both calls would be different based on the logic that was added for work profiles (MT calls associated with target phone account handle user while MO calls are associated with the profile user). As a result, resetting the adapter puts Telecom in a
state where it is unable to update the existing calls. This is being fixed in packages to ensure that MT calls adhere to the profile association as well, so Telecom would not try to set the adapter again in InCallController.

Bug: 294699269
Test: Manual
Test: New unit test to verify that call updates are persevered when
MO/MT call are placed from the secondary/guest user.

Change-Id: Ic771acab949f2ee6b47a5a32ffb02c0cddf0a8dc