* return false in cChunkMap::GetBlockTypeMeta if requested height is invalid
* add checks to users of cWorld::GetBlockTypeMeta
* add checks for invalid height to cChunkMap::GetBlock and cChunkMap::GetBlockMeta
* add hle0 to CONTRIBUTORS
* Fix merge conflict with isValidHeight
* Add initialisation contract and fulfil it.
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Co-authored-by: Alexander Harkness <me@bearbin.net>