check for duplicate consensus state ids (#66)

* check for duplicate consensus state ids

* clippy

ismp/src/handlers/consensus.rs

@@ -115,6 +115,10 @@ where
     // check that we have an implementation of this client
     host.consensus_client(message.consensus_client_id)?;
 
+    if host.consensus_client_id(message.consensus_state_id).is_some() {
+        Err(Error::DuplicateConsensusStateId { consensus_state_id: message.consensus_state_id })?
+    }
+
     // Store the initial state for the consensus client
     host.store_consensus_state(message.consensus_state_id, message.consensus_state)?;
     host.store_unbonding_period(message.consensus_state_id, message.unbonding_period)?;