This patch adds the necessary condition to avoid creating useless
values in fields that have eval=uniqueInPid.
The behaviour is triggered when moving records around in BE.

This empty-check is already present in other places, but was
obviously forgotten to be added to fixUniqueInPid().

Releases: master, 6.2
Resolves: #59224
Change-Id: Ie7d99f40facfd603c783f3dcca30b8f8b253fe09
Reviewed-on: http://review.typo3.org/38413


Reviewed-by: Andreas Fernandez <andreas.fernandez@aspedia.de>
Tested-by: Andreas Fernandez <andreas.fernandez@aspedia.de>
Reviewed-by: Jo Hasenau <info@cybercraft.de>
Tested-by: Jo Hasenau <info@cybercraft.de>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>