patch 9.0.0751: 'scrolloff' does not work well with 'smoothscroll'

Problem:    'scrolloff' does not work well with 'smoothscroll'.
Solution:   Make positioning the cursor a bit better.  Rename functions.
diff --git a/src/popupwin.c b/src/popupwin.c
index f9cbcef..9bc3174 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -1403,8 +1403,7 @@
 	// "margin_width" is added to "len" where it matters.
 	if (wp->w_width < maxwidth)
 	    wp->w_width = maxwidth;
-	len = win_linetabsize(wp, lnum, ml_get_buf(wp->w_buffer, lnum, FALSE),
-							      (colnr_T)MAXCOL);
+	len = linetabsize(wp, lnum);
 	wp->w_width = w_width;
 
 	if (wp->w_p_wrap)