fix: truncate when reverting writes during NetworkBehaviour synchronize (#2749)

* fix

truncate buffer back to the position.

* style

adding comment

* update

adding change log entry

Author: NoelStephensUnity

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -8,9 +8,14 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ## [Unreleased]
 
+### Added
+
 ### Fixed
 
 - Fixed a bug where having a class with Rpcs that inherits from a class without Rpcs that inherits from NetworkVariable would cause a compile error. (#2751)
+- Fixed issue where `NetworkBehaviour.Synchronize` was not truncating the write buffer if nothing was serialized during `NetworkBehaviour.OnSynchronize` causing an additional 6 bytes to be written per `NetworkBehaviour` component instance. (#2749)
+
+### Changed
 
 ## [1.7.0] - 2023-10-11
 

com.unity.netcode.gameobjects/Runtime/Core/NetworkBehaviour.cs

@@ -993,6 +993,8 @@ internal bool Synchronize<T>(ref BufferSerializer<T> serializer, ulong targetCli
                 if (finalPosition == positionBeforeSynchronize || threwException)
                 {
                     writer.Seek(positionBeforeWrite);
+                    // Truncate back to the size before
+                    writer.Truncate();
                     return false;
                 }
                 else