AttributeError when removing interior ring

Occurred while processing `https://sentinel-s2-l1c.s3.amazonaws.com/tiles/21/N/VH/2016/12/7/0/tileInfo.json`

Full stack trace

```
Traceback (most recent call last):
File "main.py", line 316, in
main()
File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 716, in __call__
return self.main(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 696, in main
rv = self.invoke(ctx)
File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 889, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 534, in invoke
return callback(*args, **kwargs)
File "main.py", line 312, in main
range_metadata(start, end, folder, concurrency, writers, geometry_check=geometry_check)
File "/ad/site-packages/sentinel_s3/main.py", line 192, in range_metadata
num_worker_threads))
File "/ad/site-packages/sentinel_s3/main.py", line 135, in daily_metadata
counter = product_metadata(product, product_dir, counter, writers, geometry_check)
File "/ad/site-packages/sentinel_s3/main.py", line 81, in product_metadata
metadata = tile_metadata(tile_info.json(), copy(product_metadata), geometry_check)
File "/ad/site-packages/sentinel_s3/converter.py", line 303, in tile_metadata
meta = get_tile_geometry_from_s3(meta)
File "/ad/site-packages/sentinel_s3/converter.py", line 241, in get_tile_geometry_from_s3
meta['tile_data_geometry']) = get_tile_geometry(f, epsg_code(meta['tile_geometry']))
File "/ad/site-packages/sentinel_s3/converter.py", line 217, in get_tile_geometry
data_geojson = mapping(data_shape)
File "/usr/local/lib/python2.7/dist-packages/shapely/geometry/geo.py", line 75, in mapping
return ob.__geo_interface__
File "/usr/local/lib/python2.7/dist-packages/shapely/geometry/polygon.py", line 300, in __geo_interface__
coords = [tuple(self.exterior.coords)]
AttributeError: 'NoneType' object has no attribute 'coords'
```