[0.79] Added catch for rare case of NoTree datalayer causing array index out of bounds

When WorldGenGrowTrees tries to place a sapling there is a small chance (unsure of actual chance) that it can pick a region with a tree datalayer of "NoTree" (DataLayer: line 34).  I'm not sure if it actually supposed to be able to get this layer, but I had a world that did generate with it (I unfortunately don't have the world/seed anymore).

In the case where it picks this datalayer, EnumTree.values() will throw an array index error, so I just told the code to ignore this layer if it encounters it.