Fixed crash on unknown biome.

[madmaxoft]

Fixes #179.

[madmaxoft]

This is a hotfix for the problem so that it doesn't seem to happen anymore, but still technically the code is broken, because QHash is not guaranteed to be thread-safe. On the other hand, locking the hash for querying biome in every pixel would be too much of a performance hit.

[EtlamGit]

Could you please also make this method const?

[madmaxoft]

Here you go.

(compile-checked only on MSVC 2017)

[EtlamGit]

Great! And you found even more methods to be set to const.

[madmaxoft]

const usually grows like cancer, they had to be const-ed in order to use the const return value.