"appendFile" doesn't throw an error if the path contains dot

[prokopsimek]

Hi, memfs doesn't throw an error when you want to create file with fn "appendFile" with path containing dots.

Current test:

it('Reject when trying to write on a directory', () => {
      const vol = new Volume();
      const { promises } = vol;
      vol.fromJSON({
        '/foo': null,
      });
      return expect(promises.appendFile('/foo', 'bar')).rejects.toBeInstanceOf(Error);
    });

src.: https://github.com/streamich/memfs/blob/master/src/tests/promises.test.ts#L263

Should be added one more test smth like:

it('Reject when trying to write on a file with non existing parental directory containing dots', () => {
      const vol = new Volume();
      const { promises } = vol;
      vol.fromJSON();
      return expect(promises.appendFile('/foo.ts/bar.ts', '...')).rejects.toBeInstanceOf(Error);
    });

The problem is in the path: '/foo.ts/bar.ts'. The parental directory does not exist, but if you call:

const stats1 = await promises.lstat('/foo.ts')
stats1.isFile() // returns true, but should be false, it should be directory

const stats2 = await promises.lstat('/foo.ts/bar.ts')
stats2.isFile() // returns true

Correct behavior: Should return an error ENOTDIR: not a directory, rmdir '.../foo.ts'