Do not launch assistant via long press when device is locked.

            case LONG_PRESS_BACK_NOTHING:

                break;

            case LONG_PRESS_BACK_GO_TO_VOICE_ASSIST:

                final boolean keyguardActive = mKeyguardDelegate == null

                        ? false

                        : mKeyguardDelegate.isShowing();

                if (!keyguardActive) {

                    Intent intent = new Intent(Intent.ACTION_VOICE_ASSIST);

                    startActivityAsUser(intent, UserHandle.CURRENT_OR_SELF);

                }

                break;

        }

    }