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.
diff --git a/src/arglist.c b/src/arglist.c
index 503cbd9..79628fd 100644
--- a/src/arglist.c
+++ b/src/arglist.c
@@ -557,6 +557,8 @@
 
     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 @@
 
     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);