Fix display of mode line when the right divider is used

Fix display of mode line when the right divider is used

* src/xdisp.c (init_iterator): For the mode-line, adjust
last_visible_x due to the right divider and the 'box' attribute,
if any, of the mode-line face.
(display_min_width): Update current_x after producing the stretch
glyph, to mimic PRODUCE_GLYPHS.
(display_mode_line): Widen the last glyph to account for adding
the right box line to it.  (Bug#5930)