Fix TrustedCredentialsSettings NPE

[Cause of Defect]
TrustedCredentialsSettings#mKeyChainConnectionByProfileId is get/set by
more than one thread. Main thread would set it in onDestroy method, and
AsyncTask would get and set in the doInBackground method. So
mKeyChainConnectionByProfileId.get(profileId) would get null after
onDestroy method get called.

Bug: N/A
Test: Debugger to simulate concurrency
Change-Id: I0664d1e9b88b079855354ce0e6fe014a98a22327
Signed-off-by: daqi <daqi@xiaomi.com>