Fix issue 10 - check serialized size before writing to stream
diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
index c498245..f3e012a 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
@@ -112,6 +112,7 @@
     }
     
     public override void WriteTo(pb::CodedOutputStream output) {
+      int size = SerializedSize;
       if (HasOptionalMessage) {
         output.WriteMessage(1, OptionalMessage);
       }