vim-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.
73a16c22a4

src/nvim/testdir/test_cmdline.vim

@@ -2024,6 +2024,15 @@ func Test_wildmenu_pum()
   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')

test/functional/ui/popupmenu_spec.lua

@@ -2160,6 +2160,38 @@ describe('builtin popupmenu', function()
 
     feed('<esc>')
 
+    -- Check "list" still works
+    command('set wildmode=longest,list')
+    feed(':cn<Tab>')
+    screen:expect([[
+                                      |
+      {1:~                               }|
+      {1:~                               }|
+      {1:~                               }|
+      {4:                                }|
+      :cn                             |
+      cnewer       cnoreabbrev        |
+      cnext        cnoremap           |
+      cnfile       cnoremenu          |
+      :cn^                             |
+    ]])
+    feed('s')
+    screen:expect([[
+                                      |
+      {1:~                               }|
+      {1:~                               }|
+      {1:~                               }|
+      {4:                                }|
+      :cn                             |
+      cnewer       cnoreabbrev        |
+      cnext        cnoremap           |
+      cnfile       cnoremenu          |
+      :cns^                            |
+    ]])
+
+    feed('<esc>')
+    command('set wildmode=full')
+
     -- check positioning with multibyte char in pattern
     command("e långfile1")
     command("sp långfile2")
@@ -2229,11 +2261,12 @@ describe('builtin popupmenu', function()
       :b långfile^                                       |
     ]])
 
-    -- special case: when patterns ends with "/", show menu items aligned
-    -- after the "/"
     feed('<esc>')
     command("close")
     command('set wildmode=full')
+
+    -- special case: when patterns ends with "/", show menu items aligned
+    -- after the "/"
     feed(':e compdir/<tab>')
     screen:expect([[
                                                         |