💩 zb: Panic on client handshake w/ extra bytes after handshake

There is something strange happening with gdbus so this commit is to
check what bytes we're left with after handshake that causes the issue.

zbus/src/connection/handshake.rs

@@ -467,6 +467,13 @@ impl Handshake for ClientHandshake {
             }
         }
 
+        if !self.common.recv_buffer.is_empty() {
+            panic!(
+                "Received extra data from the server: {:?}",
+                self.common.recv_buffer
+            );
+        }
+
         trace!("Handshake done");
         let (read, write) = self.common.socket.take();
         Ok(Authenticated {