Protect box ids access, Bump libosmium version

[patrickbr]

This PR contains the stuff added during the debug process for #80 that we should keep in master. This mainly includes some safeguards in areaInAreaApprox and boxIdIsect which explicitly catch and handle situations that should never happen, but might.

I also bumped the libosmium version to v2.20.0

Note that the segfaults in #80 were not related to these changes. The reason for them is still unknown, but they were only reproducible with Boost 1.78, not with previous or later versions.