patch 8.2.3884: crash when clearing the argument list while using it

Problem:    Crash when clearing the argument list while using it.
Solution:   Lock the argument list for ":all".

src/arglist.c

@@ -910,6 +910,7 @@ do_arg_all(
     tabpage_T	*old_curtab, *last_curtab;
     win_T	*new_curwin = NULL;
     tabpage_T	*new_curtab = NULL;
+    int		prev_arglist_locked = arglist_locked;
 
 #ifdef FEAT_CMDWIN
     if (cmdwin_type != 0)
@@ -936,6 +937,7 @@ do_arg_all(
     // watch out for its size to be changed.
     alist = curwin->w_alist;
     ++alist->al_refcount;
+    arglist_locked = TRUE;
 
     old_curwin = curwin;
     old_curtab = curtab;
@@ -1155,6 +1157,7 @@ do_arg_all(
 
     // Remove the "lock" on the argument list.
     alist_unlink(alist);
+    arglist_locked = prev_arglist_locked;
 
     --autocmd_no_enter;
 

src/testdir/test_arglist.vim

@@ -583,4 +583,11 @@ func Test_all_not_allowed_from_cmdwin()
   au! BufEnter
 endfunc
 
+func Test_clear_arglist_in_all()
+  n 0 00 000 0000 00000 000000
+  au! * 0 n 0
+  all
+  au! *
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3884,
 /**/
     3883,
 /**/