Prevent inclusion of null KeyphraseMetadata in info map.

If getKeyphraseMetadataFromApplicationInfo encountered a parse error, it
would return a null KeyphraseMetadata instance. Other parts of
KeyphraseEnrollmentInfo assume that everything inserted into the member
mKeyphrasePackageMap is valid, so this would cause an NPE.

Bug:33448806
Test: Build a bogus enrollment APK and not see a crash.
Change-Id: I0936439ea4bd0050580a7b0ee8f08f2992ebfd63