patch 9.1.0380: Calculating line height for unnecessary amount of lines

Problem:  Calculating line height for unnecessary amount of lines with
          half-page scrolling (zhscn, after 9.1.0280)
Solution: Replace "limit_winheight" argument with higher resolution
          "max" argument to which to limit the calculated line height
          in plines_m_win() to (Luuk van Baal)

fixes: #14650
closes: #14652

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 1b6e003..9bdd46f 100644
--- a/src/move.c
+++ b/src/move.c
@@ -1455,7 +1455,7 @@
 
 	is_folded = hasFoldingWin(wp, lnum, &lnum, NULL, TRUE, NULL);
 #endif
-	row = plines_m_win(wp, wp->w_topline, lnum - 1, FALSE);
+	row = plines_m_win(wp, wp->w_topline, lnum - 1, INT_MAX);
 	// "row" should be the screen line where line "lnum" begins, which can
 	// be negative if "lnum" is "w_topline" and "w_skipcol" is non-zero.
 	row -= adjust_plines_for_skipcol(wp);
@@ -3219,12 +3219,18 @@
 
 	int curscount = count;
 	// Adjust count so as to not reveal end of buffer lines.
-	if (dir == FORWARD)
+	if (dir == FORWARD
+		    && (curwin->w_topline + curwin->w_height + count > buflen
+#ifdef FEAT_FOLDING
+							|| hasAnyFolding(curwin)
+#endif
+	   ))
 	{
 	    int n = plines_correct_topline(curwin, curwin->w_topline, FALSE);
 	    if (n - count < curwin->w_height && curwin->w_topline < buflen)
-		n += plines_m_win(curwin, curwin->w_topline + 1, buflen, FALSE);
-	    if (n - count < curwin->w_height)
+		n += plines_m_win(curwin, curwin->w_topline + 1, buflen,
+						    curwin->w_height + count);
+	    if (n < curwin->w_height + count)
 		count = n - curwin->w_height;
 	}