Add one more line to render loop to avoid lines to "pop in" in case visible lines use less space than control dimensions
fixed handling of linespacing (was inconsistant and not working properly);
fixed juddering (now smooth scrolling possible even when using bigger fonts, faster scrolling speed and linespacing set)
Merge remote-tracking branch 'remotes/origin/BUG-4172-Text_in_scrollbox_pops_in_on_the_bottom_rather_than_scroll_in'