patch 8.2.0418: code in eval.c not sufficiently covered by tests

Problem:    Code in eval.c not sufficiently covered by tests.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #5815)
diff --git a/src/testdir/test_window_cmd.vim b/src/testdir/test_window_cmd.vim
index 77e58d2..ceba4be 100644
--- a/src/testdir/test_window_cmd.vim
+++ b/src/testdir/test_window_cmd.vim
@@ -546,6 +546,11 @@
   call assert_equal(59, line("w0"))
   call assert_equal('59 ', s3)
 
+  %d
+  call setline(1, ['one', 'two', 'three'])
+  call assert_equal(1, line('w0'))
+  call assert_equal(3, line('w$'))
+
   bwipeout!
   call test_garbagecollect_now()
 endfunc