findPackageConfigFile crashes when given a missing or deleted Directory #163901
Description
I've seen this come up in refactoring tests, but not in real code, and I think it's a bug:
import 'package:file/file.dart';
import 'package:flutter_tools/src/dart/package_map.dart' show findPackageConfigFile;
void example(FileSystem fileSystem) {
// Pick a clearly non-existent directory.
final Directory directory = fileSystem.directory('i/do/not/exist');
print(findPackageConfigFile(directory)); // Expected: null, but throws
}This is because fileSystem.identicalSync throws if one or more of the paths are missing, and is used and I think this can be fixed by ensuring the path being checked actually exists (if it doesn't, then continue looking).