patch 8.2.0921: CTRL-W T in cmdline window causes trouble

Problem:    CTRL-W T in cmdline window causes trouble.
Solution:   Disallow CTRL-W T in the cmdline window.  Add more tests.
            (Naruhiko Nishino, closes #6219)

src/testdir/test_cmdline.vim

@@ -1503,6 +1503,27 @@ func Test_cmdwin_blocked_commands()
   call assert_fails('call feedkeys("q:Q\<CR>", "xt")', 'E11:')
   call assert_fails('call feedkeys("q:Z\<CR>", "xt")', 'E11:')
   call assert_fails('call feedkeys("q:\<F1>\<CR>", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>s", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>v", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>^", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>n", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>z", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>o", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>w", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>j", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>k", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>h", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>l", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>T", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>x", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>r", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>R", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>K", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>}", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>]", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>f", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>d", "xt")', 'E11:')
+  call assert_fails('call feedkeys("q:\<C-W>g", "xt")', 'E11:')
 endfunc
 
 " Close the Cmd-line window in insert mode using CTRL-C

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    921,
 /**/
     920,
 /**/

src/window.c

@@ -340,6 +340,7 @@ do_window(
 
 // move window to new tab page
     case 'T':
+		CHECK_CMDWIN;
 		if (one_window())
 		    msg(_(m_onlyone));
 		else