fix(options): 'scrolloffpad' reads the wrong window #41684

Problem:
`get_scrolloffpad_value()` takes a window, but its else branch reads
`curwin->w_p_sop` instead of `wp->w_p_sop`.

Reachable from Vimscript, since `line('w0', winid)` runs
`update_topline()` on another window without making it current.

Solution:
Read the option from the window that was passed in.

AI-assisted

src/nvim/option.c

@@ -7151,7 +7151,7 @@ int64_t get_scrolloff_value(win_T *wp)
 /// global value when appropriate.
 int64_t get_scrolloffpad_value(win_T *wp)
 {
-  return wp->w_p_sop == -1 ? p_sop : curwin->w_p_sop;
+  return wp->w_p_sop == -1 ? p_sop : wp->w_p_sop;
 }
 
 /// Return the effective 'sidescrolloff' value for the current window, using the