Add some sanity checks to the Sapling1 pickBlock() function.

Closes #276

src/main/java/forestry/arboriculture/gadgets/BlockSapling.java

@@ -149,6 +149,8 @@ public class BlockSapling extends BlockTreeContainer {
 	@Override
 	public ItemStack getPickBlock(MovingObjectPosition target, World world, int x, int y, int z) {
 		TileSapling sapling = getSaplingTile(world, x, y, z);
+		if (sapling == null || sapling.getTree() == null)
+			return null;
 		return PluginArboriculture.treeInterface.getMemberStack(sapling.getTree(), EnumGermlingType.SAPLING.ordinal());
 	}