Camera2: Always disconnect in the client destructor

If Camera2Client failed to initialize, it would skip disconnect step,
and thus the camera would be forever marked as busy. By always calling
disconnect it will always call free.

It also adds a new guarantee that Client::disconnect is idempotent

Bug: 7298182
Change-Id: Ic9876f1665b7d9b3c0da692880f63f165e3f4fa5