method destroy may delete everything in the table

[wishper]

Hi, thanks for fixing #37
However, the fix changed a bit the behaviour of destroy function
Previously, if record was unsaved, it correctly threw an exception

After #37 , unsaved record have typeof this.id === 'object', so does not fire the exception

However, the deleteRecords function does not find the id, and so it does not create the 'where' clause, executing "delete from "