Fixed random NPE on startup

src/main/java/net/minecraft/server/WorldServer.java

@@ -75,10 +75,12 @@ public class WorldServer extends World {
 
         if (block != null) {
             // CraftBukkit start
-            BlockPhysicsEvent event = new BlockPhysicsEvent(Event.Type.BLOCK_PHYSICS, world.getBlockAt(i1, j1, k1), l1);
-            server.getPluginManager().callEvent(event);
-            if (event.isCancelled()) {
-                return;
+            if (world != null) {
+                BlockPhysicsEvent event = new BlockPhysicsEvent(Event.Type.BLOCK_PHYSICS, world.getBlockAt(i1, j1, k1), l1);
+                server.getPluginManager().callEvent(event);
+                if (event.isCancelled()) {
+                    return;
+                }
             }
             // CraftBukkit stop