Fix issue 10 - check serialized size before writing to stream
diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
index 82dec7a..43a98a4 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
@@ -99,6 +99,7 @@
     }
     
     public override void WriteTo(pb::CodedOutputStream output) {
+      int size = SerializedSize;
       if (HasD) {
         output.WriteInt32(1, D);
       }