Fix value range of ns in RandFst().

ns must not be zero. Otherwise the ns_dist creation

	std::uniform_int_distribution<StateId> ns_dist(0, ns - 1);

might be invalid. This patch ensures that ns is >= 0.

diff -upr openfst-1.8.2.orig/src/include/fst/test/rand-fst.h openfst-1.8.2/src/include/fst/test/rand-fst.h
--- openfst-1.8.2.orig/src/include/fst/test/rand-fst.h	2023-07-16 20:46:34.154919412 +0200
+++ openfst-1.8.2/src/include/fst/test/rand-fst.h	2023-07-16 20:46:40.598277091 +0200
@@ -44,7 +44,7 @@ void RandFst(const int num_random_states
 
   std::mt19937_64 rand(seed);
   const StateId ns =
-      std::uniform_int_distribution<>(0, num_random_states - 1)(rand);
+      std::uniform_int_distribution<>(1, num_random_states - 1)(rand);
   std::uniform_int_distribution<size_t> arc_dist(0, num_random_arcs - 1);
   std::uniform_int_distribution<Label> label_dist(0, num_random_labels - 1);
   std::uniform_int_distribution<StateId> ns_dist(0, ns - 1);