Fix crash when creating custom timer in the start view

LeCountdown/LeCountdownApp.swift

@@ -40,6 +40,7 @@ struct LeCountdownApp: App {
                 .environment(\.managedObjectContext, persistenceController.container.viewContext)
                 .fullScreenCover(isPresented: $showStartView) {
                     StartView(isPresented: $showStartView)
+                        .environment(\.managedObjectContext, persistenceController.container.viewContext)
                 }
             .onAppear {
                 self._onAppear()

LeCountdown/Views/StartView.swift

@@ -9,6 +9,7 @@ import SwiftUI
 
 struct StartView: View {
     
+    @Environment(\.managedObjectContext) private var viewContext
     @StateObject var model: PresetSelectionModel = PresetSelectionModel()
     
     @Binding var isPresented: Bool
@@ -40,6 +41,7 @@ struct StartView: View {
                 .background(Color.accentColor)
             }.sheet(isPresented: self.$showAddScreen) {
                 NewCountdownView(isPresented: $showAddScreen)
+                    .environment(\.managedObjectContext, viewContext)
             }
 
             Button {