patch 8.2.0644: insufficient testing for invalid function arguments

Problem:    Insufficient testing for invalid function arguments.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #5988)
diff --git a/src/testdir/test_menu.vim b/src/testdir/test_menu.vim
index 85d54f0..4fd2828 100644
--- a/src/testdir/test_menu.vim
+++ b/src/testdir/test_menu.vim
@@ -255,6 +255,7 @@
   nmenu Test.abc  <Nop>
   call assert_equal('<Nop>', menu_info('Test.abc').rhs)
   call assert_fails('call menu_info([])', 'E730:')
+  call assert_fails('call menu_info("", [])', 'E730:')
   nunmenu Test
 
   " Test for defining menus in different modes