[Settings] Fix crashes caused by null bluetooth adapter and ethernet

manager

Emulator system image doesn't support bluetooth and ethernet manager
yet.
BUG: 150408099

Signed-off-by: Weilun Du <wdu@google.com>
Change-Id: Iab4f7b962f01755fe7d84956f9b54374f1e17408
(cherry picked from commit 08e95d0d)