Fix the `GAWK Grammar' failure.

* src/LR0.c (final_state): Initialize to -1 so that we do compute
the reductions of the first state which was mistakenly confused
with the final state because precisely final_state was initialized
to 0.
* tests/sets.at (Nullable): Adjust: state 0 does have lookaheads,
now noticed by Bison.
* tests/regression.at (Rule Line Numbers): Adjust: state 0 does
have a reduction on $default.

tests/regression.at

@@ -328,6 +328,8 @@ state 0
 
     'a' 	shift, and go to state 1
 
+    $default	reduce using rule 3 (@2)
+
     expr	go to state 2
     @2  	go to state 3
 

tests/sets.at

@@ -158,7 +158,11 @@ transpose: output
   0:
 
 Lookaheads: BEGIN
-State 0: 0 lookaheads
+State 0: 1 lookaheads
+   on 0 ($) -> rule -4
+   on 1 (error) -> rule -4
+   on 2 ($undefined.) -> rule -4
+   on 3 ('e') -> rule -4
 State 1: 0 lookaheads
 State 2: 0 lookaheads
 State 3: 0 lookaheads