Workaround for a stupid compiler reporting potential null-pointer dereference

example/kalman_filter-alpha_beta_filter_example2.cpp

@@ -62,9 +62,11 @@ int main()
 
   std::vector<state> track(num_measurements);
 
-  // We need an initial estimate of track[0] as there is no previous state to get a prediction from
-  track[0].range.estimated_current_state = 30'000q_m;
-  track[0].speed.estimated_current_state = 40.0q_mps;
+  if(track.size() > 0) { 
+    // We need an initial estimate of track[0] as there is no previous state to get a prediction from
+    track[0].range.estimated_current_state = 30'000q_m;
+    track[0].speed.estimated_current_state = 40.0q_mps;
+  }
 
   for (auto n = 0U; n < num_measurements; ++n) {
     if (n > 0) {