Fix disagreement of client_id/app_data pointer semantic

KM1/KM2 implementations should treat nullptr and KeymasterBlob{nullptr, 0}
equally when passed in as client_id or app_data. However, trusty KM1
treats them differently.

Bug: 113110105
Bug: 113084196
Change-Id: Ie0e2b5d60d808e4f7a8e48aeb4c694268f9bc0a1