[file_selector] Avoids using path_provider in web example app. (#4445)

This is a minor change to the `file_selector` example app to prevent it from using `path_provider` when running on the web (because `path_provider` isn't available on the web).

Fixes flutter/flutter#130368

(PS: This should be exempt from publishing requirements, because the modified file is not shown in pub.dev, or anywhere else AFAIK.)

Author: ditman

-

@@ -5,7 +5,7 @@
 import 'package:file_selector/file_selector.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
-import 'package:path_provider/path_provider.dart';
+import 'package:path_provider/path_provider.dart' as path_provider;
 
 /// Page for showing an example of saving with file_selector
 class SaveTextPage extends StatelessWidget {
@@ -21,9 +21,11 @@ class SaveTextPage extends StatelessWidget {
     final String fileName = _nameController.text;
     // This demonstrates using an initial directory for the prompt, which should
     // only be done in cases where the application can likely predict where the
-    // file will be saved. In most cases, this parameter should not be provided.
-    final String initialDirectory =
-        (await getApplicationDocumentsDirectory()).path;
+    // file will be saved. In most cases, this parameter should not be provided,
+    // and in the web, path_provider shouldn't even be called.
+    final String? initialDirectory = kIsWeb
+        ? null
+        : (await path_provider.getApplicationDocumentsDirectory()).path;
     final FileSaveLocation? result = await getSaveLocation(
       initialDirectory: initialDirectory,
       suggestedName: fileName,