ltlcross: completely fix #420

Reported by Salomon Sickert.

* bin/ltlcross.cc: Also call determinize_unknown_acceptance() for
positive automata.
* tests/core/ltlcross3.test: Add another test case.
* NEWS: Mention the fix.

NEWS

@@ -45,6 +45,10 @@ New in spot 2.9.2.dev  (not yet released)
     file. With this refactoring, we can retrieve both a kripke or a
     kripkecube from a PINS file.
 
+  Bugs fixed:
+
+  - Completely fix the ltlcross issue mentionned in previous release.
+
 New in spot 2.9.2 (2020-07-21)
 
   Bugs fixed:

bin/ltlcross.cc

@@ -1531,6 +1531,7 @@ namespace
                                   << " ed.\n";
                       sm = new
                         spot::scc_info(p, spot::scc_info_options::TRACK_STATES);
+                      sm->determine_unknown_acceptance();
                     }
                   catch (const std::bad_alloc&)
                     {

tests/core/ltlcross3.test

@@ -331,6 +331,9 @@ run 0 ltlcross --verbose --no-checks -f 'FGa' 'ltl2tgba'
 # that did not exist.  Issue #420.
 ltlcross --csv=/dev/null ltl2tgba 'ltl2tgba -D -G' --states=5 \
          -f '(G(F(((a) & (X(X(a)))) | ((!(a)) & (X(X(!(a))))))))'
+# And this related one even survived in 2.9.2...
+ltlcross --csv=/dev/null ltl2tgba 'ltl2tgba -P -D' --states=45 \
+         -f 'F(G((X(X(b))) | ((c) U (X(X(d))))))'
 
 # The CSV file should not talk about product if --products=0
 ltlcross --color --products=0 ltl2tgba -f GFa -f FGa --csv=out.csv