Fix div element width if textarea has scrollbar

If the textarea contains lots of text (such that it has a vertical scrollbar) _and_ if the caret is positioned near the beginning of the text (such that the text up to the caret position would _not_ require a scrollbar) then we have to enforce a scrollbar on the "fake div".
Merge pull request #60 from Steffen185/patch-1

Fix div element width if textarea has scrollbar