ltlcross: fix swapped automata in error diagnostic

Failures could be reported against "Comp(Ni)*Comp(Pj)" when
it was really "Comp(Nj)*Comp(Pi)" that failed.

* bin/ltlcross.cc: Here.
* NEWS: Mention the bug.

NEWS

@@ -80,6 +80,12 @@ New in spot 2.0.3a (not yet released)
   * A new example page shows how to test the equivalence of
     two LTL/PSL formulas.  https://spot.lrde.epita.fr/tut04.html
 
+  Bug fixes:
+
+  * When ltlcross found a bug using a product of complemented
+    automata, the error message would report "Comp(Ni)*Comp(Pj)" as
+    non-empty while the actual culprit was "Comp(Nj)*Comp(Pi)".
+
 New in spot 2.0.3 (2016-07-11)
 
   Bug fixes:

bin/ltlcross.cc

@@ -1184,8 +1184,8 @@ namespace
                     if (comp_pos[i] && comp_neg[j] &&
                         (i == j || (!comp_neg[i] && !comp_pos[j])))
                       problems +=
-                        check_empty_prod(comp_pos[i], comp_neg[j],
-                                         i, j, true, true);
+                        check_empty_prod(comp_neg[j], comp_pos[i],
+                                         j, i, true, true);
                   }
         }
       else