When closing a connection or in case a reconnect occured all statement handles will be invalidated by setting stmt->mysql to NULL. Since applications cannot check if a reconnect has occurred (without tracking change of thread_id) they will crash when calling a prepared statement API function, since stmt->mysql became NULL.

So in the prepared statement API we should always check validity of the connection (stmt->mysql) and return a CR_SERVER_LOST error when the statement was invalidated.