ecg: don't run callback if there is no data to be processed

preload/apps/ecg/__init__.py

@@ -176,6 +176,9 @@ class ECG:
                 self.pulse = -1
 
     def callback_ecg(self, datasets):
+        if len(datasets) == 0:
+            return
+
         if self.ble_streaming:
             try:
                 self.b.gatts_notify(