ltlcross: disable products columns in CSV if --products=0

* bin/ltlcross.cc: Fix it.
* tests/core/ltlcross3.test: Test it.
* NEWS: Mention the bug.

NEWS

@@ -159,6 +159,9 @@ Bugs fixed:
     an obligation property, the result would always be a complete
     automaton even without the -C option.
 
+  * ltlcross --products=0 --csv should not output any product-related
+    column in the CSV output since it has nothing to display there.
+
 New in spot 2.2.2 (2016-12-16)
 
   Build:

bin/ltlcross.cc

@@ -497,6 +497,8 @@ parse_opt(int key, char* arg, struct argp_state*)
           ++arg;
         }
       products = to_pos_int(arg);
+      if (products == 0)
+        products_avg = false;
       break;
     case OPT_NOCHECKS:
       no_checks = true;

tests/core/ltlcross3.test

 #!/bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2012, 2013, 2014, 2015, 2016 Laboratoire de Recherche
+# Copyright (C) 2012, 2013, 2014, 2015, 2016, 2017 Laboratoire de Recherche
 # et Développement de l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -217,3 +217,8 @@ diff foo expected
 
 # This command used to crash.  Report from František Blahoudek.
 run 0 ltlcross --verbose --no-checks -f 'FGa' 'ltl2tgba'
+
+# The CSV file should not talk about product if --products=0
+ltlcross --products=0 ltl2tgba -f GFa -f FGa --csv=out.csv
+grep product out.csv && exit 1
+check_csv out.csv