Handle better finalize/last ref of model cases in ModestHeaderWindow
Handle better finalize/last ref of model cases in ModestHeaderWindow

* src/hildon2/modest-header-window.c: add different (more safe) handling
  of weak reference to model used to free signal handler of sort column
  (fixes NB#134642).

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