Resolve active call NPE in unhold

It's possible that there's no active call when unholding the current call. Resolve the NPE from referencing the call id.

Bug: 380805900
Change-Id: Ie3cae59ff0a96829ec742059bb10b9a0c5591b99
Flag: com.android.server.telecom.flags.enable_call_sequencing
Test: Manual
1 file changed