[BUGFIX] Use correct parameter type in insertPositionIcon

PagePositionMap::printContentElementsColumns must call insertPositionIcon
with fake row array instead of empty string as first parameter.

Change-Id: I11afd7e8cad47b6892f0cd60feea8b53ff4d5945
Fixes: #43284
Releases: 6.0
Reviewed-on: http://review.typo3.org/16722
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert