libs/rand: fix "out-of-memory" error on unexpected argument (#5215)

CHANGELOG_PENDING.md

@@ -19,3 +19,4 @@ Friendly reminder, we have a [bug bounty program](https://hackerone.com/tendermi
 
 - [evidence] [\#5170](https://github.com/tendermint/tendermint/pull/5170) change abci evidence time to the time the infraction happened not the time the evidence was committed on the block (@cmwaters)
 - [node] Don't attempt fast sync when the ABCI application specifies ourself as the only validator via `InitChain` (@erikgrinaker)
+- [libs/rand] [\#5215](https://github.com/tendermint/tendermint/pull/5215) Fix out-of-memory error on unexpected argument of Str() (@SadPencil)

libs/rand/random.go

@@ -149,6 +149,10 @@ func (r *Rand) Seed(seed int64) {
 
 // Str constructs a random alphanumeric string of given length.
 func (r *Rand) Str(length int) string {
+	if length <= 0 {
+		return ""
+	}
+
 	chars := []byte{}
 MAIN_LOOP:
 	for {