Fixed an error when generating thumbnails for a field which has no thumbnail config
Fixed an error when generating thumbnails for a field which has no thumbnail config

TituxMetal/CakePHP3-Proffer,hiromi2424/CakePHP3-Proffer,srubengt/CakePHP3-Proffer,Kamoris/CakePHP3-Proffer,davidyell/CakePHP3-Proffer