patch 8.1.2385: opening cmdline window with feedkeys() does not work

Problem:    Opening cmdline window with feedkeys() does not work. (Yegappan
            Lakshmanan)
Solution:   Recognize K_CMDWIN also when ex_normal_busy is set.
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 7a4979e..5e25979 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -843,3 +843,8 @@
   bwipeout bufb
   bwipeout bufc
 endfunc
+
+func Test_cmdwin_feedkeys()
+  " This should not generate E488
+  call feedkeys("q:\<CR>", 'x')
+endfunc