Remove some assertions, documents can have 0 pages. Make initial current

2005-04-16  Marco Pesenti Gritti <mpg@redhat.com>

        * backend/ev-page-cache.c: (ev_page_cache_init),
        (_ev_page_cache_new):

        Remove some assertions, documents can have 0 pages.
        Make initial current page -1.

        * shell/ev-page-action.c: (page_changed_cb):

        Show "" if current page is -1

        * shell/ev-window.c: (update_action_sensitivity),
        (ev_window_setup_document):

        When document has 0 pages do not set the view
        and make nearly everything insensitive.