ChunkStay must be disabled while being deleted.

Fixes #758.

src/LightingThread.cpp

@@ -286,6 +286,7 @@ void cLightingThread::LightChunk(cLightingChunkStay & a_Item)
 	{
 		a_Item.m_CallbackAfter->Call(a_Item.m_ChunkX, a_Item.m_ChunkZ);
 	}
+	a_Item.Disable();
 	delete &a_Item;
 }