patch 8.2.0270: some code not covered by tests

Problem:    Some code not covered by tests.
Solution:   Add test cases. (Yegappan Lakshmanan, closes #5649)
diff --git a/src/testdir/test_normal.vim b/src/testdir/test_normal.vim
index 2115c76..843374d 100644
--- a/src/testdir/test_normal.vim
+++ b/src/testdir/test_normal.vim
@@ -2006,7 +2006,7 @@
     tabclose
   endfor
   " clean up
-  call assert_fails(':tabclose', 'E784')
+  call assert_fails(':tabclose', 'E784:')
 endfunc
 
 fun! Test_normal38_nvhome()