safety check (and hopeful fix) for chunk saving

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

@@ -425,7 +425,7 @@ public class MinecraftServer implements Runnable, ICommandListener {
         Vec3D.a();
         ++this.ticks;
 
-        ((CraftScheduler) this.server.getScheduler()).mainThreadHeartbeat(this.ticks);
+        ((CraftScheduler) this.server.getScheduler()).mainThreadHeartbeat(this.ticks); // CraftBukkit
 
         for (j = 0; j < this.worlds.size(); ++j) { // CraftBukkit
             // if (j == 0 || this.propertyManager.getBoolean("allow-nether", true)) { // CraftBukkit
@@ -437,10 +437,9 @@ public class MinecraftServer implements Runnable, ICommandListener {
                         EntityPlayer entityplayer = (EntityPlayer) this.serverConfigurationManager.players.get(i);
                         entityplayer.netServerHandler.sendPacket(new Packet4UpdateTime(entityplayer.getPlayerTime())); // Add support for per player time
                     }
+                    // CraftBukkit end
                 }
 
-                // CraftBukkit end
-
                 worldserver.doTick();
 
                 while (worldserver.doLighting()) {

src/main/java/org/bukkit/craftbukkit/CraftWorld.java

@@ -153,7 +153,7 @@ public class CraftWorld implements World {
 
         net.minecraft.server.Chunk chunk = world.chunkProviderServer.getOrCreateChunk(x, z);
 
-        if (save) {
+        if (save && !chunk.isEmpty()) {
             chunk.removeEntities();
             world.chunkProviderServer.saveChunk(chunk);
             world.chunkProviderServer.saveChunkNOP(chunk);