fix(scrollbind): properly take filler/virtual lines into account

Problem:

`'scrollbind'` does not work properly if the window being scrolled
automatically contains any filler/virtual lines (except for diff filler
lines).

This is because when the scrollbind check is done, the logic only
considers changes to topline which are represented as line numbers.

Solution:

Write the logic for determine the scroll amount to take into account
filler/virtual lines.

Fixes #29751

1 files changed, 1 insertions, 1 deletions

diff --git a/src/nvim/ex_cmds.c b/src/nvim/ex_cmds.c
index 5cc9a8c106..f170fd0762 100644
--- a/src/nvim/ex_cmds.c
+++ b/src/nvim/ex_cmds.c
@@ -2695,7 +2695,7 @@ int do_ecmd(int fnum, char *ffname, char *sfname, exarg_T *eap, linenr_T newlnum
       *so_ptr = 999;    // force cursor to be vertically centered in the window
     }
     update_topline(curwin);
-    curwin->w_scbind_pos = curwin->w_topline;
+    curwin->w_scbind_pos = plines_m_win_fill(curwin, 1, curwin->w_topline);
     *so_ptr = n;
     redraw_curbuf_later(UPD_NOT_VALID);  // redraw this buffer later
   }