patch 8.2.4328: command line complete matches cleard when typing character

Problem:    Command line complete matches cleard when typing character.
            (Dominique Pellé)
Solution:   Only remove a popup menu if there is one.
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 7faf811..175647d 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -2132,6 +2132,15 @@
   call TermWait(buf)
   call VerifyScreenDump(buf, 'Test_wildmenu_pum_29', {})
 
+  " Check "list" still works
+  call term_sendkeys(buf, "\<C-U>set wildmode=longest,list\<CR>")
+  call term_sendkeys(buf, ":cn\<Tab>")
+  call TermWait(buf)
+  call VerifyScreenDump(buf, 'Test_wildmenu_pum_30', {})
+  call term_sendkeys(buf, "s")
+  call TermWait(buf)
+  call VerifyScreenDump(buf, 'Test_wildmenu_pum_31', {})
+
   call term_sendkeys(buf, "\<C-U>\<CR>")
   call StopVimInTerminal(buf)
   call delete('Xtest')