Header can be output twice in import script causing a coding_error

During the final stage of an import if the pre-check fails, rather than the cause of the failure being displayed there is a coding_error with the following message:

Coding error detected, it must be fixed by a programmer: Invalid state passed to moodle_page::set_state. We are in state 2 and state 1 was requested.

This appears to be caused because in this case the renderer is instructed to output the Moodle page header for a second time

In backup/import.php during the final stage the header is output on line 91, in the case of a pre-check fail it is output again on line 148.