Fix ArrayDdbConverter ArgumentOutOfRangeException

[jsneedles]

I was trying to do a .ToDocument call on an entity with an array property and was getting:

   at System.Collections.Generic.List`1.set_Item(Int32 index, T value)
   at EfficientDynamoDb.Internal.Converters.Collections.ArrayDdbConverter`1.Write(T[]& value)
   at EfficientDynamoDb.Internal.Metadata.DdbPropertyInfo`1.SetDocumentValue(Object obj, Document document)
   at EfficientDynamoDb.Internal.Extensions.DocumentExtensions.ToDocument[T](T entity, DynamoDbContextMetadata metadata)
   at EfficientDynamoDb.Internal.Converters.ObjectDdbConverter`1.Write(T& value)
   at EfficientDynamoDb.Internal.Metadata.DdbPropertyInfo`1.SetDocumentValue(Object obj, Document document)
   at EfficientDynamoDb.Internal.Extensions.DocumentExtensions.ToDocument[T](T entity, DynamoDbContextMetadata metadata)
   at EfficientDynamoDb.DynamoDbContext.ToDocument[T](T entity)

Dug through and found this small bug.

When doing operations directly like Batch.PutItem and similar, it seems to write just fine, so probably goes through a different code path.

[firenero]

Thanks for submitting the PR @jsneedles. There was the same bug in IReadOnlyCollectionDdbConverter.cs so I applied the same fix there.