Renders sometimes include building parts from nearby buildings

When rendering a building way, all elements that intersect the way's bounding box are fetched from the OSM API. This can include elements outside of the building perimeter -- including building parts of nearby buildings, which are added to the `parts` list and rendered.

Example: [278078955](https://www.openstreetmap.org/way/278078955) as currently rendered at https://beakerboy.github.io/OSMBuilding/index.html?info&id=278078955 also shows building parts [369862691](https://www.openstreetmap.org/way/369862691) and [369862692](https://www.openstreetmap.org/way/369862692) from building [369862694](https://www.openstreetmap.org/way/369862694) to the north. Note that it doesn't add the entire extra building -- the northernmost part [369862690](https://www.openstreetmap.org/way/369862690) is entirely outside of building 278078955's bounding box, so is not fetched.