test.py --task test updates

test.py

@@ -165,7 +165,7 @@ def test(data,
 
     # Compute statistics
     stats = [np.concatenate(x, 0) for x in zip(*stats)]  # to numpy
-    if len(stats):
+    if len(stats) and stats[0].any():
         p, r, ap, f1, ap_class = ap_per_class(*stats)
         p, r, ap50, ap = p[:, 0], r[:, 0], ap[:, 0], ap.mean(1)  # [P, R, AP@0.5, AP@0.5:0.95]
         mp, mr, map50, map = p.mean(), r.mean(), ap50.mean(), ap.mean()