[pathprovider] Fix fall through bug

[mehmetf]

No description provided.

[amirh]

LGTM

[ened]

@mehmetf @amirh how could we possibly write a test for that?
I was just working on adding test for path_provider and this did fall through! See #1990.

  test('getApplicationSupportDirectory', () async {
    final Directory result = await getApplicationSupportDirectory();
    final String uuid = Uuid().v1();
    final File file = File('${result.path}/$uuid.txt');
    file.writeAsStringSync('Hello world!');
    expect(file.readAsStringSync(), 'Hello world!');
    expect(result.listSync(), isNotEmpty);
    file.deleteSync();
  });

[rockingdice]

Any ETA about v1.2.1 of path_provider on pub?
I met this issue:
java.lang.IllegalStateException: Reply already submitted which is probably this fix can make it work.