Bugfix: TrackStatisticsUpdater was computing distance incorrectly.

While using a cycling speed and distance sensor, the updater was not using the distance from the most recent trackpoint but rather the one considered last moving.

Fixes #762.

src/androidTest/java/de/dennisguse/opentracks/content/data/TrackPointTest.java

@@ -1,10 +1,13 @@
 package de.dennisguse.opentracks.content.data;
 
+import android.location.Location;
+
 import org.junit.Test;
 
 import java.time.Instant;
 import java.time.temporal.ChronoUnit;
 
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
@@ -25,4 +28,35 @@ public class TrackPointTest {
 
         assertFalse(tp.isRecent());
     }
+
+    @Test
+    public void distanceToPrevious() {
+        Location l1 = new Location("test");
+        l1.setLatitude(0);
+        l1.setLongitude(0.0001);
+        TrackPoint tp1 = new TrackPoint(l1);
+
+        Location l2 = new Location("test");
+        l2.setLatitude(0);
+        l2.setLongitude(0.0002);
+        TrackPoint tp2 = new TrackPoint(l2);
+
+        // without sensor distance
+        assertEquals(11.13, tp2.distanceToPrevious(tp1).toM(), 0.01);
+
+        // tp1 has sensor distance
+        tp1.setSensorDistance(Distance.of(5));
+        tp1.setSensorDistance(null);
+        assertEquals(11.13, tp2.distanceToPrevious(tp1).toM(), 0.01);
+
+        // tp2 has sensor distance
+        tp1.setSensorDistance(null);
+        tp2.setSensorDistance(Distance.of(5));
+        assertEquals(5, tp2.distanceToPrevious(tp1).toM(), 0.01);
+
+        // tp1 and tp2 have sensor distance
+        tp1.setSensorDistance(Distance.of(10));
+        tp2.setSensorDistance(Distance.of(5));
+        assertEquals(5, tp2.distanceToPrevious(tp1).toM(), 0.01);
+    }
 }