patch 8.2.2837: various code lines not covered by tests

Problem:    Various code lines not covered by tests.
Solution:   Add test cases. (Dominique Pellé, closes #8178)
diff --git a/src/testdir/test_vim9_cmd.vim b/src/testdir/test_vim9_cmd.vim
index 1e1a498..080fe20 100644
--- a/src/testdir/test_vim9_cmd.vim
+++ b/src/testdir/test_vim9_cmd.vim
@@ -13,6 +13,7 @@
     vim9cm assert_equal('yes', y)
   END
   CheckScriptSuccess(lines)
+  assert_fails('vim9cmd', 'E1164:')
 enddef
 
 def Test_edit_wildcards()