Merge pull request #443 from CocoTheOwner/fixCompoundNPE

Fix NPE by checking if null before calling on it.

src/main/java/com/volmit/iris/engine/framework/EngineCompositeGenerator.java

@@ -134,7 +134,7 @@ public class EngineCompositeGenerator extends ChunkGenerator implements IrisAcce
     }
 
     public void tick() {
-        if (isClosed()) {
+        if (getComposite() == null || isClosed()) {
             return;
         }