Explicitly reset StagedRender.last_render at the end of StagedRender.initialize.

This fixes the issue, that search_refresh kept
@last_render at >=4*win.height, so that
StagedRender.is_ready? always returned false.
That way the search list was limited to only
2*win.height results after a refresh.
Merge pull request #4 from ff2000/search_paging_after_reload

Explicitly reset StagedRender.last_render at the end of StagedRender.ini...