MySql batcher may attempt initiating a new batch without closing open reader first. #1605
Description
The MySql batcher misses a CheckReaders call when it initiate a new batch, causing it to fail when a datareader is already opened (which is possible through the use of Enumerable method on queries).
This is showcased on this build, errors on Legacy fixtures. (This build has the MySql batcher enabled, while this batcher is currently by default not enabled in NHibernate tests.)