Crash when processing type=building with outline being a multipolygon

[deevroman]

https://beakerboy.github.io/OSMBuilding/?type=relation&id=19046126

/full, alas, doesn't load the relation recursively, so you can't build a bbox for it that can be passed to /map

[Beakerboy]

this seems to still be an issue.

[deevroman]

Yes, I will extract the fix from #88 for this in a separate PR