[Framework] Empty and error state handling for the Feed list (#18)

This PR contains the work done to implement the handling of empty and error states for the `FeedListViewController` view controller in the `Feed` framework.

Reviewed-on: rock-n-code/app-reviews#18
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Frameworks/Feed/Bundle/Sources/Logic/View Models/FeedListViewModel.swift

@@ -24,6 +24,7 @@ extension FeedListViewController {
         @Published var isFilterEnabled: Bool = false
         @Published var isFiltering: Bool = false
         @Published var isLoading: Bool = false
+        @Published var state: FeedListState = .initial
 
         var items: [Review] = []
         var words: [TopWord] = []
@@ -88,11 +89,14 @@ extension FeedListViewController {
                     items = filter == .all
                         ? reviewsAll
                         : reviewsFiltered[filter] ?? []
-                    
+
                     isFilterEnabled = !items.isEmpty
+                    state = items.isEmpty
+                        ? .empty
+                        : .populated
                 } catch {
-                    // TODO: handle this error gracefully.
-                    print("ERROR: \(error.localizedDescription)")
+                    items = []
+                    state = .error
                 }
 
                 isLoading = false
@@ -111,7 +115,12 @@ extension FeedListViewController {
         }
         
         func item(for index: Int) -> Review? {
-            guard index < items.count else { return nil }
+            guard
+                !items.isEmpty,
+                index < items.count
+            else {
+                return nil
+            }
             
             return isWordsShowing
                 ? items[index - 1]