Camera3: Check metadata channel before stopping it

- There is a sequence where we could open camera,
  initialize it and then close it. In this case
  the metadata channel will not get initialized.
  The destructor will try to stop it without
  checking whether it got intitilized first.

BUG: 10689446
Change-Id: I8369d04ec5275ce84603dc8a75ac6764f8407415
Signed-off-by: Iliyan Malchev <malchev@google.com>
1 file changed