[BUGFIX] Show content for columns with colPos set only

Setting up backend layouts with colPos not set will show the content of
column 0 because of an excplicit cast of the colPos. This patch checks
if colPos is set and if not skips the assignment of records.

Resolves: #91176
Releases: master, 10.4
Change-Id: I75d9818c4330bb8a4d9a7a60130a547167a83e58
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64305


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>