Fix bug in construct_nfa

Intermediate final states were being left in by add_fsa(); we always
want to mark the added FSA's final state as non-final.

lib/construct.c

@@ -25,6 +25,9 @@ static void add_fsa(fsa_t *f, const fsa_t *o, int *init_out, int *final_out)
 	}
 	memcpy(f->states + f->count, o->states, o->count * sizeof(fsa_state_t));
 
+	// Mark o's final state as non-final.
+	f->states[f->count].final = false;
+
 	// Retarget the rules of the copied states to refer to the new
 	// state indices.
 	for (int i = f->count; i < count; ++i) {