patch 9.1.1451: tabpanel rendering artifacts when scrolling

Problem:  tabpanel rendering artifacts when scrolling
Solution: update scrolling logic (Hirohito Higashi)

fixes: #17495
closes: #17496

Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/term.c b/src/term.c
index 649e483..6f7983b 100644
--- a/src/term.c
+++ b/src/term.c
@@ -4464,7 +4464,7 @@
 {
     OUT_STR(tgoto((char *)T_CS, W_WINROW(wp) + wp->w_height - 1,
 							 W_WINROW(wp) + off));
-    if (*T_CSV != NUL && wp->w_width != topframe->fr_width)
+    if (*T_CSV != NUL && wp->w_width != Columns)
 	OUT_STR(tgoto((char *)T_CSV, wp->w_wincol + wp->w_width - 1,
 							       wp->w_wincol));
     screen_start();		    // don't know where cursor is now
@@ -4478,9 +4478,7 @@
 {
     OUT_STR(tgoto((char *)T_CS, (int)Rows - 1, 0));
     if (*T_CSV != NUL)
-	OUT_STR(tgoto((char *)T_CSV,
-		    firstwin->w_wincol + topframe->fr_width - 1,
-		    firstwin->w_wincol));
+	OUT_STR(tgoto((char *)T_CSV, (int)Columns - 1, 0));
     screen_start();		    // don't know where cursor is now
 }