Handle renamed packages during default grants

If an L device has a privileged app on the system image which was
updated and an M OTA renames the app package (supported only for
privileged apps) we end up with a disabled system package setting
with no package information. Since we are not doing a null check
of the package we get from the disabled package settings during
default grants we crash leaving the system in a bad state.

bug:25687380

Change-Id: I4f2ebcaf471e4bd1696298eab4716b50c52ca5c4