patch 8.1.1299: "extends" from 'listchars' is used when 'list' is off

Problem:    "extends" from 'listchars' is used when 'list' is off. (Hiroyuki
            Yoshinaga)
Solution:   Only use the "extends" character when 'list' is on. (Hirohito
            Higashi, closes #4360)
diff --git a/src/testdir/test_listchars.vim b/src/testdir/test_listchars.vim
index 3eef75d..5df5010 100644
--- a/src/testdir/test_listchars.vim
+++ b/src/testdir/test_listchars.vim
@@ -110,6 +110,25 @@
   call cursor(1, 1)
   call assert_equal([expected], ScreenLines(1, virtcol('$')))
 
+  " test extends
+  normal ggdG
+  set listchars=extends:Z
+  set nowrap
+  set nolist
+  call append(0, [ repeat('A', &columns + 1) ])
+
+  let expected = repeat('A', &columns)
+
+  redraw!
+  call cursor(1, 1)
+  call assert_equal([expected], ScreenLines(1, &columns))
+
+  set list
+  let expected = expected[:-2] . 'Z'
+  redraw!
+  call cursor(1, 1)
+  call assert_equal([expected], ScreenLines(1, &columns))
+
   enew!
   set listchars& ff&
 endfunc