vim-patch:8.2.2463: using :arglocal in an autocommand may use freed memory

Problem:    Using :arglocal in an autocommand may use freed memory.
            (houyunsong)
Solution:   Check if the arglist is locked.
6bcb877ec1

src/nvim/arglist.c

@@ -490,6 +490,9 @@ void check_arg_idx(win_T *win)
 void ex_args(exarg_T *eap)
 {
   if (eap->cmdidx != CMD_args) {
+    if (check_arglist_locked() == FAIL) {
+      return;
+    }
     alist_unlink(ALIST(curwin));
     if (eap->cmdidx == CMD_argglobal) {
       ALIST(curwin) = &global_alist;
@@ -499,6 +502,9 @@ void ex_args(exarg_T *eap)
   }
 
   if (*eap->arg != NUL) {
+    if (check_arglist_locked() == FAIL) {
+      return;
+    }
     // ":args file ..": define new argument list, handle like ":next"
     // Also for ":argslocal file .." and ":argsglobal file ..".
     ex_next(eap);

src/nvim/testdir/test_autocmd.vim

@@ -3010,6 +3010,15 @@ func Test_Visual_doautoall_redraw()
   %bwipe!
 endfunc
 
+" This was using freed memory.
+func Test_BufNew_arglocal()
+  arglocal
+  au BufNew * arglocal
+  call assert_fails('drop xx', 'E1156:')
+
+  au! BufNew
+endfunc
+
 func Test_autocmd_closes_window()
   au BufNew,BufWinLeave * e %e
   file yyy