Fix picker never being deallocated due to retain cycle.
Fix picker never being deallocated due to retain cycle.

imjerrybao/DZNPhotoPickerController,jonesgithub/DZNPhotoPickerController,imjerrybao/DZNPhotoPickerController,dzenbot/DZNPhotoPickerController,imjerrybao/DZNPhotoPickerController,dennislysenko/DZNPhotoPickerController,imjerrybao/DZNPhotoPickerController,jonesgithub/DZNPhotoPickerController,topfreegames/TFGPhotoPickerController,jonesgithub/DZNPhotoPickerController,ndnguru/DZNPhotoPickerController,jonesgithub/DZNPhotoPickerController,dredenba/DZNPhotoPickerController,lichuanjun/DZNPhotoPickerController,ahbou/DZNPhotoPickerController