PackageManager#queryIntentServices breaks its contract.

PackageManager#queryIntentServices javadoc contract states that this
method (and the like) never returns null, rather an empty list if
no result is found. However, there is a path in the PackageManagerService
that returns null, thus breaking the contract. Handling the null list
explicitly.

bug:10930560

Change-Id: I708c51b8b7075e529145c8b0bf159efd6b697532