Check TE coordinates early and provide a meaningful error message if they're wrong

[eigenraven]

Should help diagnose this crash:

java.lang.ArrayIndexOutOfBoundsException: Index -16 out of bounds for length 4096
	at RFB-Launch//net.minecraft.world.chunk.storage.ExtendedBlockStorage.func_76665_b(SourceFile:1093)
	at RFB-Launch//net.minecraft.world.chunk.Chunk.func_76628_c(Chunk.java:548)
	at RFB-Launch//net.minecraft.world.chunk.Chunk.func_150812_a(Chunk.java:878)
	at RFB-Launch//net.minecraft.world.chunk.Chunk.func_150813_a(Chunk.java:862)
	at RFB-Launch//net.minecraft.world.chunk.storage.AnvilChunkLoader.loadEntities(AnvilChunkLoader.java:500)
	at RFB-Launch//net.minecraftforge.common.chunkio.ChunkIOProvider.callStage2(ChunkIOProvider.java:41)
	at RFB-Launch//net.minecraftforge.common.chunkio.ChunkIOProvider.callStage2(ChunkIOProvider.java:12)
	at RFB-Launch//net.minecraftforge.common.util.AsynchronousExecutor$Task.finish(AsynchronousExecutor.java:189)
	at RFB-Launch//net.minecraftforge.common.util.AsynchronousExecutor.finishActive(AsynchronousExecutor.java:354)
	at RFB-Launch//net.minecraftforge.common.chunkio.ChunkIOExecutor.tick(ChunkIOExecutor.java:30)
	at RFB-Launch//net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:596)
	at RFB-Launch//net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:334)
	at RFB-Launch//net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:547)
	at RFB-Launch//net.minecraft.server.MinecraftServer.run(MinecraftServer.java:427)
	at RFB-Launch//net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)