readmsg: minor fix

* readmsg/readmsg.c: Bail out unless arguments are present.
* doc/texinfo/programs.texi: Update.

@@ -4853,6 +4853,11 @@ Note that it will not match a message containing @samp{Staff Meeting}
 which matches the pattern is printed.
 @end enumerate
 
+Unless one of the informational options is used, at least one command
+line argument must be present.  Informational options are:
+@option{--help} (@option{-?}), @option{--usage}, and
+@option{--version} (@option{-V}).
+
 @menu
 * Opt-readmsg::   Invocation of @command{readmsg}.
 * Conf-readmsg::  Configuration of @command{readmsg}.

@@ -297,6 +297,14 @@ main (int argc, char **argv)
 		   argc, argv, 0, &index, NULL))
     exit (1);
 
+  argc -= index;
+
+  if (argc == 0)
+    {
+      mu_error (_("not enough arguments"));
+      exit (1);
+    }
+
   status = mu_mailbox_create_default (&mbox, mailbox_name);
   if (status != 0)
     {
@@ -367,8 +375,6 @@ main (int argc, char **argv)
     }
 
   /* Build an array containing the message number.  */
-  argc -= index;
-  if (argc > 0)
   msglist (mbox, show_all, argc, &argv[index], &set, &n);
 
   for (i = 0; i < n; ++i)