[BUGFIX] Show error message in page module for invalid backend layout

If there is a backend layout selected with no colPos defined inside the backend layout option, then the page
module fatals with an error.

A error message is now shown to display that at least one
colPos parameter must be set.

Resolves: #67276
Releases: master
Change-Id: I02120be981607d35efa31f49cc0ee4cc992172e4
Reviewed-on: https://review.typo3.org/45146


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Josef Glatz <josef.glatz@typo3.org>
Reviewed-by: Frans Saris <franssaris@gmail.com>
Tested-by: Frans Saris <franssaris@gmail.com>