Fix bug with feedback loop during shutdown

- Use height to indicate tip change by comparing heights
- Give undefined for callback when shutting down

integration/regtest.js

@@ -235,7 +235,7 @@ describe('Daemon Binding Functionality', function() {
   describe('tip updates', function() {
     it('will get an event when the tip is new', function(done) {
       this.timeout(4000);
-      bitcoind.once('tip', function(height) {
+      bitcoind.on('tip', function(height) {
         height.should.equal(152);
         done();
       });

lib/daemon.js

@@ -10,8 +10,6 @@ var $ = bitcore.util.preconditions;
 
 var daemon = Daemon;
 
-
-
 function Daemon(options) {
   var self = this;
 
@@ -202,22 +200,20 @@ Daemon.prototype.start = function(options, callback) {
     });
 
     bitcoindjs.onBlocksReady(function(err, result) {
-      self.emit('ready', result);
-    });
 
-    function onTipUpdateListener(err, result) {
-      if (err) {
-        self.emit('error', err);
-      } else {
-        // Emit and event that the tip was updated
-        self.emit('tip', result);
+      function onTipUpdateListener(result) {
+        if (result) {
+          // Emit and event that the tip was updated
+          self.emit('tip', result);
+          // Recursively wait until the next update
+          bitcoindjs.onTipUpdate(onTipUpdateListener);
+        }
       }
 
-      // Recursively wait until the next update
       bitcoindjs.onTipUpdate(onTipUpdateListener);
-    }
 
-    bitcoindjs.onTipUpdate(onTipUpdateListener);
+      self.emit('ready', result);
+    });
 
     setTimeout(function callee() {
       // Wait until wallet is loaded:

src/bitcoindjs.cc

@@ -229,9 +229,9 @@ static void
 async_tip_update(uv_work_t *req) {
   async_tip_update_data *data = static_cast<async_tip_update_data*>(req->data);
 
-  int64_t nLastBest = nTimeBestReceived;
+  size_t lastHeight = chainActive.Height();
 
-  while(nLastBest == nTimeBestReceived && !shutdown_complete) {
+  while(lastHeight == (size_t)chainActive.Height() && !shutdown_complete) {
     usleep(1E6);
   }
 
@@ -246,10 +246,13 @@ async_tip_update_after(uv_work_t *req) {
   async_tip_update_data *data = static_cast<async_tip_update_data*>(req->data);
 
   Local<Function> cb = data->callback.Get(isolate);
-  const unsigned argc = 2;
+  const unsigned argc = 1;
+  Local<Value> result = Undefined(isolate);
+  if (!shutdown_complete) {
+    result = NanNew<Number>(data->result);
+  }
   Local<Value> argv[argc] = {
-    v8::Null(isolate),
-    Local<Value>::New(isolate, NanNew<Number>(data->result))
+    Local<Value>::New(isolate, result)
   };
   TryCatch try_catch;
   cb->Call(isolate->GetCurrentContext()->Global(), argc, argv);
@@ -259,7 +262,6 @@ async_tip_update_after(uv_work_t *req) {
 
   delete data;
   delete req;
-
 }
 
 NAN_METHOD(OnBlocksReady) {