Fix RT-DETR exported onnx model (#3317)

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

ultralytics/nn/modules/head.py

@@ -270,7 +270,7 @@ class RTDETRDecoder(nn.Module):
         anchors = torch.cat(anchors, 1)  # (1, h*w*nl, 4)
         valid_mask = ((anchors > eps) * (anchors < 1 - eps)).all(-1, keepdim=True)  # 1, h*w*nl, 1
         anchors = torch.log(anchors / (1 - anchors))
-        anchors = torch.where(valid_mask, anchors, torch.inf)
+        anchors = anchors.masked_fill(~valid_mask, float('inf'))
         return anchors, valid_mask
 
     def _get_encoder_input(self, x):
@@ -294,7 +294,7 @@ class RTDETRDecoder(nn.Module):
         bs = len(feats)
         # prepare input for decoder
         anchors, valid_mask = self._generate_anchors(shapes, dtype=feats.dtype, device=feats.device)
-        features = self.enc_output(torch.where(valid_mask, feats, 0))  # bs, h*w, 256
+        features = self.enc_output(valid_mask * feats)  # bs, h*w, 256
 
         enc_outputs_scores = self.enc_score_head(features)  # (bs, h*w, nc)
         # dynamic anchors + static content