Add FIXME to track silent failure on fetching collections

As collections are fetched and added to the `list` property in the CollectionListModel’s initializer, it’s tricky to throw an error here: we call it as a property initializer in CollectionListView, which cannot throw.

Consider refactoring this logic such that we’re using, for example, a @FetchRequest in CollectionListView instead.

Shared/PostCollection/CollectionListModel.swift

@@ -19,6 +19,7 @@ class CollectionListModel: NSObject, ObservableObject {
             try collectionsController.performFetch()
             list = collectionsController.fetchedObjects ?? []
         } catch {
+            // FIXME: Errors cannot be thrown out of the CollectionListView property initializer
             print("Failed to fetch collections!")
         }
     }