patch 8.2.1411: when splitting a window localdir is copied but prevdir is not

Problem:    when splitting a window localdir is copied but prevdir is not.
Solution:   Also copy prevdir. (closes #6667)
diff --git a/src/testdir/test_cd.vim b/src/testdir/test_cd.vim
index bd6e3d9..8a0fbb2 100644
--- a/src/testdir/test_cd.vim
+++ b/src/testdir/test_cd.vim
@@ -168,6 +168,15 @@
   call delete('Xdir', 'rf')
 endfunc
 
+func Test_lcd_split()
+  let curdir = getcwd()
+  lcd ..
+  split
+  lcd -
+  call assert_equal(curdir, getcwd())
+  quit!
+endfunc
+
 func Test_cd_completion()
   call mkdir('XComplDir1', 'p')
   call mkdir('XComplDir2', 'p')