[Bug] - Data source outage crashes server

[Zoriot]

The plugin should not crash the server, when the data sources are not reachable. It should just don't allow generating new chunks, without spamming the log or smt.
Also, /tpll should function well without any calls.
Handle data source outage more gracefully should be handled more gracefully in general.

Parts of it have to be implemented, in the T-- Library.

[tintinkung]

Getting unavailable chunk data runs on main thread, stalling the server, then making it force to crash after pausing all memory functions.

Common Cause:

terraplusminus-1.4.0.jar//de.btegermany.terraplusminus.gen.RealWorldGenerator.getTerraChunkData(RealWorldGenerator.java:224)
terraplusminus-1.4.0.jar//de.btegermany.terraplusminus.gen.RealWorldGenerator.generateNoise(RealWorldGenerator.java:112)

Sometime:

terraplusminus-1.4.0.jar//de.btegermany.terraplusminus.gen.tree.TreePopulator.populate(TreePopulator.java:108)

Or any other method that tries to retrieve chunk data.

de.btegermany.terraplusminus.gen.RealWorldGenerator#getTerraChunkData(RealWorldGenerator.java:224)

private CachedChunkData getTerraChunkData(int chunkX, int chunkZ) {
    try {
        return this.cache.getUnchecked(new ChunkPos(chunkX, chunkZ)).get();
    } catch (InterruptedException | ExecutionException e) {
        throw new RuntimeException("Unrecoverable exception when generating chunk data asynchronously in Terra--", e);
    }
}

Since server and chunk generations is forced to run on main thread, I have no idea if there's a way to pause chunk generations when the data source is not available.