Fix a RPC client test error when the connection is closed during sending.

We do not know anything about stream errors, so we cannot deduce whether
the stream was closed.

src/network/client.rs

         }
     }
 
+    /// Sends a packet.
+    ///
+    /// # Errors
+    ///
+    /// If the connection is closed, the function does *not* return `RPCError::Closed`, but rather
+    /// returns the corresponding stream error.
     async fn send_packet(&mut self, call: CallData<PacketType, ErrorType>) {
         // Add an ID for the outgoing packet.
         let id = self.free_ids.alloc();
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::network::test_utils::{panic_after, Pipe};
+    use crate::network::test_utils::{panic_after, Pipe, PipeError};
     use crate::network::Packet;
 
     type TestPayload = u32;
             // Client task.
             let tasks = (
                 tokio::spawn(async move {
-                    assert_eq!(client.call(42).await, Err(RPCError::Closed));
+                    let status = client.call(42).await;
+                    assert!(
+                        status == Err(RPCError::Closed)
+                            || status == Err(RPCError::Stream(PipeError::Closed))
+                    );
                 }),
                 tokio::spawn(async move {
                     drop(pipe2);