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)

1 files changed, 4 insertions, 2 deletions

diff --git a/src/dispnew.c b/src/dispnew.c
index 69c2023fdf3..53eb8984747 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;
         }
     }