Fix NPE caused by null replacedPkgSetting

replacedPkgSetting can be null if the existing package has been removed around the same time it was updated, because we only acquire mLock at the commit stage. Adding an NPE check to prevent crashes.

BUG: 403742230
FIXES: 403742230
Test: builds
Change-Id: I361836d6960fdde75357c09077ba3c382ec8a7bb