Change to initialize Refresh when the onAppear event happens so that we quit crashing on macOS

Multiplatform/Shared/MainApp.swift

@@ -29,6 +29,9 @@ struct MainApp: App {
 				.frame(minWidth: 600, idealWidth: 1000, maxWidth: .infinity, minHeight: 600, idealHeight: 700, maxHeight: .infinity)
 				.environmentObject(sceneModel)
 				.environmentObject(defaults)
+				.onAppear {
+					sceneModel.startup()
+				}
 				.sheet(isPresented: $showSheet, onDismiss: { showSheet = false }) {
 					AddWebFeedView()
 				}
@@ -155,6 +158,9 @@ struct MainApp: App {
 				.environmentObject(sceneModel)
 				.environmentObject(defaults)
 				.modifier(PreferredColorSchemeModifier(preferredColorScheme: defaults.userInterfaceColorPalette))
+				.onAppear {
+					sceneModel.startup()
+				}
 		}
 		.commands {
 			CommandGroup(after: .newItem, addition: {

Multiplatform/Shared/SceneModel.swift

@@ -17,13 +17,12 @@ final class SceneModel: ObservableObject {
 	var timelineModel: TimelineModel?
 	var articleModel: ArticleModel?
 	
-	private let refreshProgressModel: RefreshProgressModel
+	private var refreshProgressModel: RefreshProgressModel? = nil
 	
-	init(refreshProgressModel: RefreshProgressModel = RefreshProgressModel()) {
-		self.refreshProgressModel = refreshProgressModel
-		self.refreshProgressModel.$state.assign(to: self.$refreshProgressState)
+	func startup() {
+		self.refreshProgressModel = RefreshProgressModel()
+		self.refreshProgressModel!.$state.assign(to: self.$refreshProgressState)
 	}
-	
 }
 
 // MARK: SidebarModelDelegate