EnumerableSerializer incorrect output when used inside another enumeration

[ievsiukovi]

Hello, I found unexpected serialization behavior when tried to serialize complex enumerations.
For example we have a Message to serialize:

public class Message
{
  public List<Dictionary<int, int>> Items { get; set; }
}

Let's do a test (extension calls are used as a short):

public static void Main()
{
  Message example = new Message()
  {
	Items = new List<Dictionary<int, int>>()
	{
	  new Dictionary<int, int>() { { 11, 11 } },
	  new Dictionary<int, int>() { { 13, 13 } }
	}
  };
  byte[] avro = example.ToAvro(); // produced bytes: 2 4 2 2 22 22 0 2 2 0 0 
		                  // when expected is: 2 4 2 2 22 22 0 2 2 26 26 0 0
  Message back = avro.FromAvro<Message>();
}

EnumerableSerializer do unexpected break when processing a second member of a sequence.
It happens because of a serializer instance that loops over a many members.
Reset chunkCounter on every serializer block helps to correct an output.

[ievsiukovi]

a part of the next pull request #10