Fix concurrent access of current groups

pycar/src/car/tracking/lidar_cache.py

@@ -42,7 +42,7 @@ class LidarCache():
         # Batch over scans, so we don't need to do our own batching to determine groups
         # TODO: Implement custom batching, as iter_scans can be unreliable
         for scan in self.lidar.iter_scans(min_len=self.measurements):
-            print('Got %d measurments' % (len(scan)))
+            print('Got %d measurements' % (len(scan)))
             if len(scan) < self.measurements:
                 # Poor scan, likely since it was the first scan.
                 continue
@@ -90,7 +90,8 @@ class LidarCache():
     @property
     def current_scan(self):
         pointScan = tracker_pb.PointScan()
-        for group in self.currentGroups:
+        tempGroups = self.currentGroups
+        for group in tempGroups:
             for point in group.get_points():
                 pointScan.points.append(tracker_pb.Point(
                     angle=point[1], distance=point[2], group_number=group.number))