Fix a bug with the user dictionary locale.

We internally use the string "zz" to mean no locale, but
the user dictionary service does not understand that and
words added with this locale pitifully end being added to
a "zz" user dictionary, which makes no sense to the user.
This change fixes things so that words added when the
keyboard is in a "no locale" layout, the words are added
to the global, all-locales user dictionary.

Bug: 6645306
Change-Id: Iec3cdd1fe3d5bc43427a43ef9ae9bf89e12be1f2