Include client updates for supporting messages when assembling messages to relay from the operational data

.changelog/unreleased/bug-fixes/ibc-relayer/3465-3565.md

@@ -0,0 +1,4 @@
+- Fix a bug where Hermes would discard the client updates
+  corresponding to the supporting headers returned by the light
+  client when assembling messages to relay from the operational data
+  ([\#3465](https://github.com/informalsystems/hermes/issues/3465))

crates/relayer/src/link/operational_data.rs

@@ -158,26 +158,24 @@ impl OperationalData {
         relay_path: &RelayPath<ChainA, ChainB>,
     ) -> Result<TrackedMsgs, LinkError> {
         // For zero delay we prepend the client update msgs.
-        let client_update_msg = if !self.conn_delay_needed() {
+        let client_update_msgs = if !self.conn_delay_needed() {
             let update_height = self.proofs_height.increment();
 
             debug!(
                 "prepending {} client update at height {}",
                 self.target, update_height
             );
 
-            // Fetch the client update message. Vector may be empty if the client already has the header
-            // for the requested height.
-            let mut client_update_opt = match self.target {
+            // Fetch the client update messages.
+            // Vector may be empty if the client already has the header for the requested height.
+            match self.target {
                 OperationalDataTarget::Source => {
                     relay_path.build_update_client_on_src(update_height)?
                 }
                 OperationalDataTarget::Destination => {
                     relay_path.build_update_client_on_dst(update_height)?
                 }
-            };
-
-            client_update_opt.pop()
+            }
         } else {
             let (client_state, _) = match self.target {
                 OperationalDataTarget::Source => relay_path
@@ -205,12 +203,12 @@ impl OperationalData {
 
             if client_state.is_frozen() {
                 return Ok(TrackedMsgs::new(vec![], self.tracking_id));
-            } else {
-                None
             }
+
+            vec![]
         };
 
-        let msgs = client_update_msg
+        let msgs = client_update_msgs
             .into_iter()
             .chain(self.batch.iter().map(|gm| gm.msg.clone()))
             .collect();