Avoids updating path.routes while app is in background

SwiftUI will ignore the changes until the app becomes active, at which point it will
try to make all changes in one go, which might fail if the changes aren't supported
in one update.

Sources/FlowStacks/ScreenModifier.swift

@@ -4,6 +4,7 @@ import SwiftUI
 /// nested FlowStack using its parent's navigation view would not have the child's environment objects propagated to
 /// pushed screens.
 struct ScreenModifier<Data: Hashable>: ViewModifier {
+  @Environment(\.scenePhase) var scenePhase
   var path: RoutesHolder
   var destinationBuilder: DestinationBuilderHolder
   var navigator: FlowNavigator<Data>
@@ -26,6 +27,7 @@ struct ScreenModifier<Data: Hashable>: ViewModifier {
         }
       }
       .onChange(of: typedPath) { typedPath in
+        guard scenePhase == .active else { return }
         path.routes = typedPath.map { $0.erased() }
       }
       .onChange(of: path.routes) { routes in
@@ -39,5 +41,9 @@ struct ScreenModifier<Data: Hashable>: ViewModifier {
           fatalError("Cannot add \(type(of: route.screen.base)) to stack of \(Data.self)")
         }
       }
+      .onChange(of: scenePhase) { phase in
+        guard phase == .active else { return }
+        path.routes = typedPath.map { $0.erased() }
+      }
   }
 }