CollectionInputFilter should respect the keys of collectionData

Currently the CollectionInputFilter assumes that collectionData has always consecutive array keys which can be wrong.

Two changes
* Iterating over collectionData instead of a composed inputCollection
* When there are less items in collectionData than `$this->count` is set to, just mark the collection as invalid, since it doesn't make sense to add them to invalidInputs when there is no corresponding set of data.