Attribute error ('read_int32') when trying to iterate rows that include JSON columns

```
AttributeError: instance has no attribute 'read_int32'
```

My DB is an AWS RDS instance (MySQL v5.7). From the stack trace it looks like this is triggered when trying to decode the JSON column, since it's coming from the read_binary_json_type call.

For reference, my code is derived from this AWS article:
https://aws.amazon.com/blogs/database/streaming-changes-in-a-database-with-amazon-kinesis/

Start at the read_binary_json_type call identified in the stack trace and trace how BinLogPacketWrapper is used while decoding JSON columns. Reproduce the failure against a MySQL 5.7 database using the AWS Kinesis example, then verify that iterating rows containing JSON columns completes without the read_int32 AttributeError.

Written by the indexing model from the issue text.