Revise the IllegalArgumentException check

Combining the two IllegalArgumentException check in getKeySetByAlias
to mitigate the potential information leakage.

Bug: 189858116
Test: atest PackageManagerTests
Test: manually using the PoC in the buganizer to ensure the symptom
      no longer exists.
Change-Id: Id407900e156555db1ec6b87cbcd233a9976f242e