emacs-28 335a660: Fix display glitches with side-by-side windows on TTY frames

[Eli Zaretskii]

branch: emacs-28
commit 335a660b4b725eb76abfa5d80295ac5c7be5d205
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Fix display glitches with side-by-side windows on TTY frames
    
    * src/dispnew.c (adjust_glyph_matrix, prepare_desired_row): Leave
    room for the border glyph only if the window does actually have
    the right margin.  (Bug#51521)
---
 src/dispnew.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/dispnew.c b/src/dispnew.c
index 69c2023..53eb898 100644
--- a/src/dispnew.c
+++ b/src/dispnew.c
@@ -475,7 +475,8 @@ adjust_glyph_matrix (struct window *w, struct glyph_matrix 
*matrix, int x, int y
                = row->glyphs[TEXT_AREA] + dim.width - left - right;
              /* Leave room for a border glyph.  */
              if (!FRAME_WINDOW_P (XFRAME (w->frame))
-                 && !WINDOW_RIGHTMOST_P (w))
+                 && !WINDOW_RIGHTMOST_P (w)
+                 && right > 0)
                row->glyphs[RIGHT_MARGIN_AREA] -= 1;
              row->glyphs[LAST_AREA]
                = row->glyphs[LEFT_MARGIN_AREA] + dim.width;
@@ -1148,7 +1149,8 @@ prepare_desired_row (struct window *w, struct glyph_row 
*row, bool mode_line_p)
          row->glyphs[RIGHT_MARGIN_AREA] = row->glyphs[LAST_AREA] - right;
          /* Leave room for a border glyph.  */
          if (!FRAME_WINDOW_P (XFRAME (w->frame))
-             && !WINDOW_RIGHTMOST_P (w))
+             && !WINDOW_RIGHTMOST_P (w)
+             && right > 0)
            row->glyphs[RIGHT_MARGIN_AREA] -= 1;
        }
     }