patch 8.2.1040: not enough testing for movement commands

Problem:    Not enough testing for movement commands.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #6313)
diff --git a/src/testdir/test_cursor_func.vim b/src/testdir/test_cursor_func.vim
index 0ddfcda..bfb908d 100644
--- a/src/testdir/test_cursor_func.vim
+++ b/src/testdir/test_cursor_func.vim
@@ -99,6 +99,7 @@
 	\ 'curscol': wincol + 9,
 	\ 'endcol': wincol + 9}, screenpos(winid, 2, 22))
   close
+  call assert_equal({}, screenpos(999, 1, 1))
   bwipe!
 endfunc