Updated ChartView (#13)

The current implementation of empty collection check in the code depends
on size()==0 which introduces unnecessary complexity to the code. So, I
updated it with isEmpty() method which checks whether the collection is
empty or not. After this, the code should exhibit improved clarity and,
in some cases, a potential performance boost due to the constant time
complexity of the isEmpty() method. Adopting isEmpty() over size() == 0
aligns with best practices and can make future code maintenance and
modifications more straightforward.

src/main/java/de/dennisguse/opentracks/chart/ChartFragment.java

@@ -185,7 +185,7 @@ public void clearTrackPoints() {
             });
         }
     }
-
+    @Override
     public void onSampledInTrackPoint(@NonNull TrackPoint trackPoint, @NonNull TrackStatistics trackStatistics) {
         if (isResumed()) {
             ChartPoint point = ChartPoint.create(trackStatistics, trackPoint, trackPoint.getSpeed(), chartByDistance, viewBinding.chartView.getUnitSystem());
@@ -253,6 +253,7 @@ private synchronized void pauseTrackDataHub() {
     }
 
     /**
+     * @deprecated
      * Returns true if the selected track is recording.
      * Needs to be synchronized because trackDataHub can be accessed by multiple threads.
      */