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.

src/arglist.c

@@ -557,6 +557,8 @@ 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;
@@ -566,6 +568,8 @@ 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/testdir/test_autocmd.vim

@@ -2717,4 +2717,13 @@ func Test_close_autocmd_tab()
   %bwipe!
 endfunc
 
+" This was using freed memory.
+func Test_BufNew_arglocal()
+  arglocal
+  au BufNew * arglocal
+  call assert_fails('drop xx', 'E1156:')
+
+  au! BufNew
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2463,
 /**/
     2462,
 /**/