[BUGFIX] Adding new records in edit mode broken

It was not possible anymore to use the "add new record" button
in TCA select fields on records with pid > 0.

This patch makes it work again; the redirect to the original page
gets prevented when a pid is set. This was handled the same way
in 4.6 and 6.1.

Change-Id: Iec058818405385efdacaebf5080f339371356810
Resolves: #56248
Related: #54085
Releases: 6.2
Reviewed-on: https://review.typo3.org/27935
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel