twa_graph: fix precondition on set_init_state

Fixes #391.

* spot/twa/twagraph.hh: Here.
* tests/core/dualize.test, tests/python/except.py: New tests.
* NEWS: Mention the bug.

tests/core/dualize.test

@@ -1,6 +1,6 @@
 #!/bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2017 Laboratoire de Recherche et
+# Copyright (C) 2017, 2019 Laboratoire de Recherche et
 # Développement de l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -65,3 +65,80 @@ EOF
 run 0 autfilt input1 --dualize --hoaf=t | tee stdout
 diff stdout expected
 rm input1 expected stdout
+
+# issue #391
+cat >input2 <<EOF
+HOA: v1
+States: 10
+Start: 0&4
+AP: 2 "p0" "p1"
+Acceptance: 2 Inf(0) | Inf(1)
+properties: trans-labels explicit-labels trans-acc univ-branch
+--BODY--
+State: 0
+[1] 1 {0}
+[0&!1] 2 {0}
+[!1] 3
+[!1] 0
+State: 1
+[t] 1 {0}
+State: 2
+[0] 2 {0}
+State: 3
+[1] 1 {0}
+[!1] 3
+State: 4
+[0] 5 {1}
+[t] 6
+[!0] 7 {1}
+[t] 4
+State: 5
+[!0] 8 {1}
+State: 6
+[!0] 9
+State: 7
+State: 8
+[t] 8 {1}
+State: 9
+[0] 8 {1}
+[!0] 9
+--END--
+EOF
+autfilt --dualize <input2 >output2
+cat >expected2<<EOF
+HOA: v1
+States: 9
+Start: 8
+AP: 2 "p0" "p1"
+acc-name: co-Buchi
+Acceptance: 1 Fin(0)
+properties: trans-labels explicit-labels state-acc univ-branch
+--BODY--
+State: 0
+[!0&!1] 0&7
+[0&!1] 0&6&7
+State: 1
+[!0] 1&3
+[0] 1&2&3
+State: 2
+[0] 4
+State: 3
+[0] 4
+[!0] 5
+State: 4
+[t] 4
+State: 5
+[!0] 5
+State: 6 {0}
+[!0] 4
+[0] 6
+State: 7
+[!1] 7
+State: 8
+[!0] 1&3
+[t] 1&2&3
+[!0&!1] 0&7
+[!1] 0&6&7
+--END--
+EOF
+diff output2 expected2