patch 8.2.2518: 'listchars' should be window-local

Problem:    'listchars' should be window-local.
Solution:   Make 'listchars' global-local. (Yegappan Lakshmanan, Marco Hinz,
            closes #5206, closes #7850)
diff --git a/src/buffer.c b/src/buffer.c
index ca1fd36..4e4f87c 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -4549,7 +4549,7 @@
 	case STL_VIRTCOL_ALT:
 	    // In list mode virtcol needs to be recomputed
 	    virtcol = wp->w_virtcol;
-	    if (wp->w_p_list && lcs_tab1 == NUL)
+	    if (wp->w_p_list && wp->w_lcs_chars.tab1 == NUL)
 	    {
 		wp->w_p_list = FALSE;
 		getvcol(wp, &wp->w_cursor, NULL, &virtcol, NULL);