Limit detections without explicit if condition (#10502)

* limit detections without explicit if condition

Signed-off-by: Yonghye Kwon <developer.0hye@gmail.com>

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* cleanup indexing code for limit detections

Signed-off-by: Yonghye Kwon <developer.0hye@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

utils/general.py

@@ -978,8 +978,7 @@ def non_max_suppression(
         c = x[:, 5:6] * (0 if agnostic else max_wh)  # classes
         boxes, scores = x[:, :4] + c, x[:, 4]  # boxes (offset by class), scores
         i = torchvision.ops.nms(boxes, scores, iou_thres)  # NMS
-        if i.shape[0] > max_det:  # limit detections
-            i = i[:max_det]
+        i = i[:max_det]  # limit detections
         if merge and (1 < n < 3E3):  # Merge NMS (boxes merged using weighted mean)
             # update boxes as boxes(i,4) = weights(i,n) * boxes(n,4)
             iou = box_iou(boxes[i], boxes) > iou_thres  # iou matrix