sbacc: fix a typo and remove some useless code

* spot/twaalgos/sbacc.cc: Do not assign to one_in twice, and
fix the value of init_acc.
* tests/core/sbacc.test: Add a test case.
* NEWS: Mention the bug.

tests/core/sbacc.test

@@ -1,6 +1,6 @@
 #! /bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2015, 2016 Laboratoire de Recherche et Développement
+# Copyright (C) 2015, 2016, 2017 Laboratoire de Recherche et Développement
 # de l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -76,6 +76,22 @@ State: 1 {0}
 State: 2
 [0] 0 {1}
 --END--
+/* The following example used to be converted into a
+   3-state automaton instead of just 2 states, due to
+   a typo in the code. */
+HOA: v1
+States: 2
+Start: 1
+AP: 2 "a" "b"
+Acceptance: 2 Fin(0) & Inf(1)
+--BODY--
+State: 0
+[t] 0 {0}
+State: 1
+[1] 0
+[0&!1] 1 {1}
+--END--
+
 EOF
 
 run 0 $autfilt --state-based-acceptance in.hoa -H > out.hoa
@@ -96,6 +112,20 @@ State: 1 {0}
 State: 2 {0 1}
 [0] 0
 --END--
+HOA: v1
+States: 2
+Start: 0
+AP: 2 "a" "b"
+acc-name: Rabin 1
+Acceptance: 2 Fin(0) & Inf(1)
+properties: trans-labels explicit-labels state-acc deterministic
+--BODY--
+State: 0 {1}
+[0&!1] 0
+[1] 1
+State: 1
+[t] 1
+--END--
 EOF
 
 diff out.hoa expected
@@ -103,7 +133,7 @@ diff out.hoa expected
 $autfilt --sba -H expected > out.hoa
 diff out.hoa expected
 
-$autfilt --strip-acc -H expected > out.hoa
+$autfilt --strip-acc -H expected -n1 > out.hoa
 cat >expected <<EOF
 HOA: v1
 States: 3