patch 9.1.0407: Stuck with long line and half-page scrolling

Problem:  No scrolling happens with half-page scrolling with line
          filling entire window when 'smoothscroll' is disabled.
          (Mathias Rav, after v9.1.0285)
Solution: Adjust amount to move cursor by so that it is moved the same
          number of lines as was scrolled, even when scrolling different
          number of lines than requested with 'nosmoothscroll'.

fixes: #14743
closes: #14746

Signed-off-by: Luuk van Baal <luukvbaal@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/move.c b/src/move.c
index 7971848..3e589ca 100644
--- a/src/move.c
+++ b/src/move.c
@@ -3158,9 +3158,10 @@
 
 /*
  * Scroll "count" lines with 'smoothscroll' in direction "dir". Return TRUE
- * when scrolling happened.
+ * when scrolling happened. Adjust "curscount" for scrolling different amount of
+ * lines when 'smoothscroll' is disabled.
  */
-static int scroll_with_sms(int dir, long count)
+static int scroll_with_sms(int dir, long count, long *curscount)
 {
     int		prev_sms = curwin->w_p_sms;
     colnr_T	prev_skipcol = curwin->w_skipcol;
@@ -3183,7 +3184,10 @@
 	    fixdir = dir * -1;
 	while (curwin->w_skipcol > 0
 	    && curwin->w_topline < curbuf->b_ml.ml_line_count)
+	{
 	    scroll_redraw(fixdir == FORWARD, 1);
+	    *curscount += (fixdir == dir ? 1 : -1);
+	}
     }
     curwin->w_p_sms = prev_sms;
 
@@ -3220,7 +3224,7 @@
 	    curwin->w_p_scr = MIN(curwin->w_height, count);
 	count = MIN(curwin->w_height, curwin->w_p_scr);
 
-	int curscount = count;
+	long curscount = count;
 	// Adjust count so as to not reveal end of buffer lines.
 	if (dir == FORWARD
 		    && (curwin->w_topline + curwin->w_height + count > buflen
@@ -3240,7 +3244,7 @@
 	// (Try to) scroll the window unless already at the end of the buffer.
 	if (count > 0)
 	{
-	    nochange = scroll_with_sms(dir, count);
+	    nochange = scroll_with_sms(dir, count, &curscount);
 	    curwin->w_cursor.lnum = prev_lnum;
 	    curwin->w_cursor.col = prev_col;
 	    curwin->w_curswant = prev_curswant;
@@ -3259,7 +3263,7 @@
 	// Scroll [count] times 'window' or current window height lines.
 	count *= ((ONE_WINDOW && p_window > 0 && p_window < Rows - 1) ?
 				MAX(1, p_window - 2) : get_scroll_overlap(dir));
-	nochange = scroll_with_sms(dir, count);
+	nochange = scroll_with_sms(dir, count, &count);
 
 	// Place cursor at top or bottom of window.
 	validate_botline();