Fix Unicode string null termination in StringToBytes method

Co-authored-by: rkttu <1297346+rkttu@users.noreply.github.com>

Author: Copilot

Experimental.System.Messaging/Messaging/Message.cs

@@ -2416,10 +2416,11 @@ internal static string StringFromBytes(byte[] bytes, int len)
         /// <internalonly/>        
         internal static byte[] StringToBytes(string value)
         {
-            int size = value.Length * 2 + 1;
+            int size = value.Length * 2 + 2;
             byte[] byteBuffer = new byte[size];
-            byteBuffer[size - 1] = 0;
             Encoding.Unicode.GetBytes(value.ToCharArray(), 0, value.Length, byteBuffer, 0);
+            byteBuffer[size - 2] = 0;
+            byteBuffer[size - 1] = 0;
             return byteBuffer;
         }