Fixes regression where current line highlight no longer extends
into the gutter area. The highlight now starts from 0 instead of
xmargin_beg, making it extend all the way to the left edge.
This restores the 4.5.1 behavior where the current line highlight
spans the entire line including the gutter area and left margin.
(cherry picked from commit 4dfbd909acc7e20d5b58bc5a135509ad97499956)
Manik Sharma
21e93094c5