[BUGFIX] IRRE creates new records when using foreign_selector

This patch links existing child records correctly to the parent IRRE
field when selecting it in the generated dropdown.

Scenario:

Parent table configuration:
====================================================
[...]['columns']['irreField']['config'] = array(
  'type' => 'inline',
  'foreign_table' => 'childTable',
  'foreign_selector' => 'childSelector',
);

Child table configuration:
====================================================
[...]['columns'][childSelector']['config'] = array(
  'type' => 'select',
  'foreign_table' => 'childTable',
);

What happens?
====================================================
1. The parent IRRE field renders a dropdown field
   before the child records
2. Selecting one of the items in the dropdown should
   link this child record to current IRRE field
3. Without patch, it will only create a blank child
   record
4. Using the patch, it will link the existing child
   to the parent IRRE field

Resolves: #43239
Releases: 6.2, 6.1
Change-Id: I2a308cb050962b71e9ba28b64a44962c91bde440
Reviewed-on: https://review.typo3.org/16690
Reviewed-by: Markus Klein
Tested-by: Markus Klein