(mail_copy0): Make sure we really got the message.

@@ -72,7 +72,16 @@ mail_copy0 (int argc, char **argv, int mark)
 
   for (mp = msglist; mp; mp = mp->next)
     {
-      mailbox_get_message (mbox, mp->msg_part[0], &msg);
+      int status;
+      
+      status = mailbox_get_message (mbox, mp->msg_part[0], &msg);
+      if (status)
+	{
+	  util_error ("can't get message %d: %s",
+		      mp->msg_part[0],
+		      mu_errstring (status));
+	  break;
+	}
       mailbox_append_message (mbx, msg);
 
       message_size (msg, &size);