null check for building pulled

src/engine/net/client/handlers/AttackCmdMsgHandler.java

@@ -58,6 +58,8 @@ public class AttackCmdMsgHandler extends AbstractClientMsgHandler {
                 break;
             case Building:
                 target = BuildingManager.getBuilding(msg.getTargetID());
+                if(target == null)
+                    return true;// early exit for no building pulled
                 Building targetBuilding = (Building) target;
                 if (!targetBuilding.isVulnerable() || targetBuilding.getRank() < 0)
                     return true;// cannot attack destroyed building or protected building