Added `try` clause to safely ignore this vanilla bug:

java.lang.NullPointerException
 	at net.minecraft.world.chunk.Chunk.func_76592_a(Chunk.java:758)
 	at net.minecraft.world.World.func_72832_d(World.java:558)
 	at assets.natureoverhaul.TreeUtils.growTree(TreeUtils.java:314)
 	at assets.natureoverhaul.NatureOverhaul.grow(NatureOverhaul.java:392)
 	at assets.natureoverhaul.NatureOverhaul.onUpdateTick(NatureOverhaul.java:169)
 	at assets.natureoverhaul.NatureOverhaul.tickEnd(NatureOverhaul.java:1060)
 	at cpw.mods.fml.common.SingleIntervalHandler.tickEnd(SingleIntervalHandler.java:34)
 	at cpw.mods.fml.common.FMLCommonHandler.tickEnd(FMLCommonHandler.java:141)
 	at cpw.mods.fml.common.FMLCommonHandler.onPostWorldTick(FMLCommonHandler.java:282)
 	at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:675)
 	at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:585)
 	at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:175)
 	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:482)
 	at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:582)