[BUGFIX] Empty columns in Page Module view cause warnings

The iteration over columns in the page module layout view
expects arrays. Since it might happen, that there is no element
for a particular column, variables need to be initialized with
an empty array.

Change-Id: I63b4b26a87f1520139c9d66d0c096a78d39e409c
Fixes: #47529
Releases: 6.2, 6.1, 6.0, 4.7, 4.5
Reviewed-on: https://review.typo3.org/20229
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader