Allow 3-point segments (#6938)

May resolve https://github.com/ultralytics/yolov5/issues/6931

utils/datasets.py

@@ -906,7 +906,7 @@ def verify_image_label(args):
             nf = 1  # label found
             with open(lb_file) as f:
                 lb = [x.split() for x in f.read().strip().splitlines() if len(x)]
-                if any([len(x) > 8 for x in lb]):  # is segment
+                if any(len(x) > 6 for x in lb):  # is segment
                     classes = np.array([x[0] for x in lb], dtype=np.float32)
                     segments = [np.array(x[1:], dtype=np.float32).reshape(-1, 2) for x in lb]  # (cls, xy1...)
                     lb = np.concatenate((classes.reshape(-1, 1), segments2boxes(segments)), 1)  # (cls, xywh)