patch 9.0.1279: display shows lines scrolled down erroneously

Problem:    Display shows lines scrolled down erroneously. (Yishai Lerner)
Solution:   Do not change "wl_lnum" at index zero. (closes #11938)
diff --git a/src/testdir/test_move.vim b/src/testdir/test_move.vim
index 98c7665..0412097 100644
--- a/src/testdir/test_move.vim
+++ b/src/testdir/test_move.vim
@@ -1,5 +1,8 @@
 " Test the ":move" command.
 
+source check.vim
+source screendump.vim
+
 func Test_move()
   enew!
   call append(0, ['line 1', 'line 2', 'line 3'])
@@ -43,4 +46,25 @@
   %bwipeout!
 endfunc
 
+func Test_move_undo()
+  CheckRunVimInTerminal
+
+  let lines =<< trim END
+      call setline(1, ['First', 'Second', 'Third', 'Fourth'])
+  END
+  call writefile(lines, 'Xtest_move_undo.vim', 'D')
+  let buf = RunVimInTerminal('-S Xtest_move_undo.vim', #{rows: 10, cols: 60, statusoff: 2})
+
+  call term_sendkeys(buf, "gg:move +1\<CR>")
+  call VerifyScreenDump(buf, 'Test_move_undo_1', {})
+
+  " here the display would show the last few lines scrolled down
+  call term_sendkeys(buf, "u")
+  call term_sendkeys(buf, ":\<Esc>")
+  call VerifyScreenDump(buf, 'Test_move_undo_2', {})
+
+  call StopVimInTerminal(buf)
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab