Avoid race conditions between queries and closing of the auto_dict database.

Keep a reference to the openhelper around across locale and input language
changes. Also, share the openhelper between the queries and updates. Creating
a new one in a separate thread could cause it to be closed at the wrong time.

Monkey bugs, probably dupes.

Bug: 2560471
Bug: 2544169
Change-Id: I6eb39145de7191732ddde455728bf147a2d1ba31