[BUGFIX] Fix negativ pid when doing a positioned insert

If you insert a content element (or a page) at a concrete position f.e.
after content element 15 the value in $row['pid'] is -15.
But in $this->data we already have the real pid, so we can just use it.

Resolves: #72751
Releases: master,7.6
Change-Id: Ib441dacf68eebd377f48589b7aeff6af1159263d
Reviewed-on: https://review.typo3.org/45969


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>