Make Explosion remember whether it was canceled so that WorldServer can avoid sending unneeded explode packets.

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

@@ -29,6 +29,7 @@ public class Explosion {
     public Entity e;
     public float f;
     public Set g = new HashSet();
+    public boolean wasCanceled = false;
 
     public Explosion(World world, Entity entity, double d0, double d1, double d2, float f) {
         this.i = world;
@@ -199,6 +200,7 @@ public class Explosion {
         server.getPluginManager().callEvent(event);
 
         if (event.isCancelled()) {
+            wasCanceled = true;
             return;
         }
         // CraftBukkit end

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

@@ -113,6 +113,12 @@ public class WorldServer extends World implements BlockChangeDelegate {
     public Explosion a(Entity entity, double d0, double d1, double d2, float f, boolean flag) {
         Explosion explosion = super.a(entity, d0, d1, d2, f, flag);
 
+        // Craftbukkit start
+        if(explosion.wasCanceled) {
+            return explosion;
+        }
+        // Craftbukkit end
+
         this.D.f.a(d0, d1, d2, 64.0D, new Packet60Explosion(d0, d1, d2, f, explosion.g));
         return explosion;
     }