Availability counts broken

[esoterik]

Discovered today:

In the cart validations, we call count on a list of reservations, expecting it to behave like Enumerable#count, but the object is actually an ActiveRecordRelation so the method behaves differently. (The block we pass isn't taken into account; we just get the size of the relation instead of the count we're expecting).

We need to convert the collection to an array before calling count; we should also make sure that this error isn't elsewhere in the code.

The issue is not occurring on deployed instances, fortunately.