fix(fastBufferWriter): wrong size passed to unsafe memset (#1453)

Apparently caused no problems in the editor, but produced some random crashes in development build

Co-authored-by: Markus Kark <markus.kark@gmail.com>

Author: andrews-unity

com.unity.netcode.gameobjects/Runtime/Serialization/FastBufferWriter.cs

@@ -189,7 +189,7 @@ internal unsafe void Grow(int additionalSizeRequired)
             var newSize = Math.Min(desiredSize, Handle->MaxCapacity);
             byte* newBuffer = (byte*)UnsafeUtility.Malloc(newSize, UnsafeUtility.AlignOf<byte>(), Handle->Allocator);
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
-            UnsafeUtility.MemSet(newBuffer, 0, sizeof(WriterHandle) + newSize);
+            UnsafeUtility.MemSet(newBuffer, 0, newSize);
 #endif
             UnsafeUtility.MemCpy(newBuffer, Handle->BufferPointer, Length);
             if (Handle->BufferGrew)