GH-1076: Fix bro_srandom() to replace 0 seeds with 1

The bro_prng() implementation cannot generate 0 as a result since it
causes every subsequent number from the PRNG to also be 0, so use the
number 1 instead of 0.

src/util.cc

@@ -1072,7 +1072,7 @@ static unsigned int first_seed = 0;
 
 static void bro_srandom(unsigned int seed, bool deterministic)
 	{
-	bro_rand_state = seed;
+	bro_rand_state = seed == 0 ? 1 : seed;
 	bro_rand_determistic = deterministic;
 
 	srandom(seed);
@@ -1081,7 +1081,7 @@ static void bro_srandom(unsigned int seed, bool deterministic)
 void bro_srandom(unsigned int seed)
 	{
 	if ( bro_rand_determistic )
-		bro_rand_state = seed;
+		bro_rand_state = seed == 0 ? 1 : seed;
 	else
 		srandom(seed);
 	}

testing/btest/Baseline/bifs.rand/out.4

@@ -0,0 +1,6 @@
+0
+131
+755
+4
+634
+473

testing/btest/bifs/rand.zeek

@@ -2,9 +2,12 @@
 # @TEST-EXEC: zeek -b %INPUT >out
 # @TEST-EXEC: zeek -b %INPUT do_seed=F >out.2
 # @TEST-EXEC: unset ZEEK_SEED_FILE && zeek -b %INPUT real_random=T >out.3
+# @TEST-EXEC: for i in $(seq 21); do echo 0 >>random-zero.seed; done
+# @TEST-EXEC: ZEEK_SEED_FILE=random-zero.seed zeek -b %INPUT >out.4
 # @TEST-EXEC: btest-diff out
 # @TEST-EXEC: btest-diff out.2
 # @TEST-EXEC: btest-diff out.3
+# @TEST-EXEC: btest-diff out.4
 
 const do_seed = T &redef;
 const real_random = F &redef;