Ensure that disable is enqueued

We are getting a NPE trying to read an arraylist of callbacks while it
is being modified in a different thread. This code path is the only one
that uses "handleMessage" which directly invokes the message. We need to
have this conform to the pattern to ensure that the list read/write is
synchronized.

Fixes: 324867208
Test: atest CommandQueueTest
Test: adb stop start and observe that boot works properly.
Flag: NONE
Change-Id: Ie4f0450239223482463957050f385283cbd03f0c