Fix sharing to the app

It's super hacky, but since I broke it, I just want to first fix it, and
later I'll try to make it nicer.

lib/app.dart

@@ -297,10 +297,12 @@ class _JournalAppState extends State<JournalApp> {
       debugShowCheckedModeBanner: false,
       //debugShowMaterialGrid: true,
       onGenerateRoute: (rs) {
-        var r = router.generateRoute(
+        var r = router
-            rs, stateContainer, _sharedText, _sharedImages);
+            .generateRoute(rs, stateContainer, _sharedText, _sharedImages, () {
           _sharedText = null;
           _sharedImages = null;
+        });
+
         return r;
       },
     );

lib/app_router.dart

@@ -42,6 +42,7 @@ class AppRouter {
     Repository repository,
     String sharedText,
     List<String> sharedImages,
+    Function callbackIfUsedShared,
   ) {
     var route = routeSettings.name;
     if (route == '/folders' || route == '/tags' || route == '/filesystem') {
@@ -53,6 +54,7 @@ class AppRouter {
           settings,
           sharedText,
           sharedImages,
+          callbackIfUsedShared,
         ),
         transitionsBuilder: (_, anim, __, child) {
           return FadeTransition(opacity: anim, child: child);
@@ -68,6 +70,7 @@ class AppRouter {
         settings,
         sharedText,
         sharedImages,
+        callbackIfUsedShared,
       ),
     );
   }
@@ -78,6 +81,7 @@ class AppRouter {
     Settings settings,
     String sharedText,
     List<String> sharedImages,
+    Function callbackIfUsedShared,
   ) {
     switch (route) {
       case '/':
@@ -126,6 +130,8 @@ class AppRouter {
         });
       }
 
+      callbackIfUsedShared();
+
       var folder = getFolderForEditor(settings, rootFolder, et);
       return NoteEditor.newNote(
         folder,