patch 9.0.0293: messages window not hidden when starting a command line

Problem:    Messages window not hidden when starting a command line.
Solution:   Hide the messages window. (closes #10996)
diff --git a/src/testdir/test_messages.vim b/src/testdir/test_messages.vim
index bb761ab..00e942e 100644
--- a/src/testdir/test_messages.vim
+++ b/src/testdir/test_messages.vim
@@ -398,6 +398,11 @@
   if using_popupwin
     redraw
     call assert_equal('test echo', Screenline(&lines))
+
+    " check that the popup is cleared when entering a command line
+    call feedkeys(':', 'xt')
+    redraw
+    call assert_equal('~', Screenline(&lines))
   else
     call assert_equal(116, screenchar(&lines, 1))
   endif