patch 8.2.4865: :startinsert right after :stopinsert may not work

Problem:    :startinsert right after :stopinsert does not work when popup menu
            is still visible.
Solution:   Use ins_compl_active() instead of pum_visible(). (closes #10352)
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index 75ec03c..6bb4997 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -555,6 +555,15 @@
   call delete('Xpumscript')
 endfunc
 
+func Test_complete_stopinsert_startinsert()
+  nnoremap <F2> <Cmd>startinsert<CR>
+  inoremap <F2> <Cmd>stopinsert<CR>
+  " This just checks if this causes an error
+  call feedkeys("i\<C-X>\<C-N>\<F2>\<F2>", 'x')
+  nunmap <F2>
+  iunmap <F2>
+endfunc
+
 func Test_pum_with_folds_two_tabs()
   CheckScreendump