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.

src/LR0.c

@@ -34,7 +34,14 @@
 #include "reduce.h"
 
 int nstates;
-int final_state;
+/* Initialize the final state to -1, otherwise, it might be set to 0
+   by default, and since we don't compute the reductions of the final
+   state, we end up not computing the reductions of the initial state,
+   which is of course needed.
+
+   FINAL_STATE is properly set by new_state when it recognizes the
+   accessing symbol: EOF.  */
+int final_state = -1;
 static state_t *first_state = NULL;
 
 static state_t *this_state = NULL;