Sync headers in ModestHeaderWindow dispose instead of finalize.
Sync headers in ModestHeaderWindow dispose instead of finalize.

* src/hildon2/modest-header-window.c: sync header changes on dispose of
  header window instead of finalize, as now, the folder in header view
  is unreferenced in dispose stage, and then sync was not working
  (fixes NB#138247).

community-ssu/modest,community-ssu/modest,community-ssu/modest,community-ssu/modest