fix zero labels (#10820)

utils/augmentations.py

@@ -201,7 +201,7 @@ def random_perspective(im,
     # Transform label coordinates
     n = len(targets)
     if n:
-        use_segments = any(x.any() for x in segments)
+        use_segments = any(x.any() for x in segments) and len(segments) == n
         new = np.zeros((n, 4))
         if use_segments:  # warp segments
             segments = resample_segments(segments)  # upsample