Only decode EXT1 tag when it is available.

Normally ADN record is stored in two tags, EFADN_TAG and EFEXT1_TAG. But if the EFEXT1_TAG is not set in EF_PBR entry,
it shouldn't be decoded otherwise it causes NullPointerException in readAdnFileAndWait().

bug: 3376954
Change-Id: I744cf5cb8662c75be1e7c6219fa92c67bdda82f2