Conference calling crash on null call object

After conference call ends there are some NPE happening because the call
is being accessed after getting destroyed. Check that underlying call
object is not NULL

Bug: b/34983172
Test: Hangup conference call from CarKitt
Change-Id: I08bfc5478a4dce4e608d7dc5cf9688b65fbc6637
1 file changed
tree: f297ce0de0352815f35f8afc53658835e8b444db
  1. android/