runtime-rs: check peer close in log_forwarder

The log_forwarder task does not check if the peer has closed, causing a
meaningless loop during the period of “kata vm exit”, when the peer
closed, and “ShutdownContainer RPC received” that aborts the log forwarder.

This patch fixes the problem.

Fixes: #7741

Signed-off-by: Zixuan Tan <tanzixuan.me@gmail.com>

src/runtime-rs/crates/agent/src/log_forwarder.rs

@@ -64,8 +64,7 @@ impl LogForwarder {
                     Ok(stream) => {
                         let stream = BufReader::new(stream);
                         let mut lines = stream.lines();
-                        while let Ok(line) = lines.next_line().await {
-                            if let Some(l) = line {
+                        while let Ok(Some(l)) = lines.next_line().await {
                             match parse_agent_log_level(&l) {
                                 LOG_LEVEL_TRACE => trace!(sl!(), "{}", l),
                                 LOG_LEVEL_DEBUG => debug!(sl!(), "{}", l),
@@ -76,7 +75,6 @@ impl LogForwarder {
                             }
                         }
                     }
-                    }
                     Err(err) => {
                         warn!(logger, "connect agent vsock failed: {:?}", err);
                     }