[BUGFIX] Migrate contentObjectRenderer data only when array

Passed $data in start method could be a non-array, e.g. in fluid
CObjectViewHelper or in extensions. Migrate $data only if it's a
not empty array and the table is set.

Makes the fieldArray fallback to TSFE->page in getData working again.

Change-Id: I469e8fa6131579a2de399516c65f4822275b187b
Fixes: #43068
Fixes: #43055
Releases: 6.0
Reviewed-on: http://review.typo3.org/16546
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel