patch 8.2.2454: leading space can not be made visible

Problem:    Leading space can not be made visible.
Solution:   Add "lead:" to 'listchars'. (closes #7772)
diff --git a/src/testdir/test_listchars.vim b/src/testdir/test_listchars.vim
index d7658bf..69c98b9 100644
--- a/src/testdir/test_listchars.vim
+++ b/src/testdir/test_listchars.vim
@@ -110,6 +110,35 @@
 	      \ '.....h>-$',
 	      \ 'iii<<<<><<$', '$'], l)
 
+  " Test lead and trail
+  normal ggdG
+  set listchars&
+  set listchars+=lead:>,trail:<,space:x
+  set list
+
+  call append(0, [
+	      \ '    ffff    ',
+	      \ '          gg',
+	      \ 'h           ',
+	      \ '            ',
+	      \ '    0  0    ',
+	      \ ])
+
+  let expected = [
+	      \ '>>>>ffff<<<<$',
+	      \ '>>>>>>>>>>gg$',
+	      \ 'h<<<<<<<<<<<$',
+	      \ '<<<<<<<<<<<<$',
+	      \ '>>>>0xx0<<<<$',
+              \ '$'
+	      \ ]
+  redraw!
+  for i in range(1, 5)
+    call cursor(i, 1)
+    call assert_equal([expected[i - 1]], ScreenLines(i, virtcol('$')))
+  endfor
+
+  call assert_equal(expected, split(execute("%list"), "\n"))
 
   " test nbsp
   normal ggdG