Fixed random NPE on startup

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

@@ -75,11 +75,13 @@ public class WorldServer extends World {
 
         if (block != null) {
             // CraftBukkit start
+            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
 
             block.b(this, i1, j1, k1, l1);