Add assertion for non-zero trust-level in Tendermint client initializ…

…ation (#1698)

* Add assertion for non-zero trust-level in Tendermint client initialization

* Add .changelog entry

.changelog/unreleased/bug-fixes/ibc/1697-assert-non-zero-trust-level.md

@@ -0,0 +1,2 @@
+- Add missing assertion for non-zero trust-level in Tendermint client initialization.
+  ([#1697](https://github.com/informalsystems/ibc-rs/issues/1697))

modules/src/clients/ics07_tendermint/client_state.rs

@@ -84,6 +84,14 @@ impl ClientState {
             ));
         }
 
+        // `TrustThreshold` is guaranteed to be in the range `[0, 1)`, but a `TrustThreshold::ZERO`
+        // value is invalid in this context
+        if trust_level == TrustThreshold::ZERO {
+            return Err(Error::validation(
+                "ClientState trust-level cannot be zero".to_string(),
+            ));
+        }
+
         // Disallow empty proof-specs
         if proof_specs.is_empty() {
             return Err(Error::validation(