Audio focus: fix mapping of old requestAudioFocus to AudioFocusRequest

When translating a focus request from the N- API to AudioFocusRequest,
  do not do null checks for listener or handler, those are only
  for the AudioFocusRequest.Builder.

Test: use app built for N- and request focus, no crash
Bug 37855238

Change-Id: I675b3144e913ab674fe27f9f65ee7a7bea24a72c