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)
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index b5e316c..94cb827 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -1503,6 +1503,27 @@
   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
diff --git a/src/version.c b/src/version.c
index c400df4..ec6117f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    921,
+/**/
     920,
 /**/
     919,
diff --git a/src/window.c b/src/window.c
index 931d86b..095eabe 100644
--- a/src/window.c
+++ b/src/window.c
@@ -340,6 +340,7 @@
 
 // move window to new tab page
     case 'T':
+		CHECK_CMDWIN;
 		if (one_window())
 		    msg(_(m_onlyone));
 		else