Fix farming NPE (#18)

Author: tier940

src/main/java/com/github/gtexpert/gtbm/integration/forestry/loaders/FFMFarmingLoader.java

@@ -18,6 +18,7 @@ public class FFMFarmingLoader {
 
     public static void init() {
         IFarmRegistry farmRegistry = ForestryAPI.farmRegistry;
+        if (farmRegistry == null) return;
 
         // GregTech Rubber tree farm
         IFarmProperties ceuFarm = ForestryFarmHelper.registerFarmType("farmCEu", FarmLogicCEu::new,

src/main/java/com/github/gtexpert/gtbm/integration/forestry/util/ForestryFarmHelper.java

@@ -18,9 +18,11 @@
 
 public class ForestryFarmHelper {
 
+    @javax.annotation.Nullable
     public static IFarmProperties registerFarmType(String farmId,
                                                    BiFunction<IFarmProperties, Boolean, IFarmLogic> logicFactory,
                                                    EnumElectronTube tube) {
+        if (ForestryAPI.farmRegistry == null) return null;
         IFarmProperties farm = ForestryAPI.farmRegistry.registerLogic(farmId, logicFactory);
         farm.registerSoil(new ItemStack(Blocks.DIRT),
                 Block.getBlockFromItem(Mods.Forestry.getItem("humus").getItem()).getDefaultState());