Update loss.py with if self.gr < 1: (ultralytics#7087)

* Update loss.py with `if self.gr < 1:`

* Update loss.py

Author: glenn-jocher

utils/loss.py

@@ -139,11 +139,13 @@ def __call__(self, p, targets):  # predictions, targets
                 lbox += (1.0 - iou).mean()  # iou loss
 
                 # Objectness
-                score_iou = iou.detach().clamp(0).type(tobj.dtype)
+                iou = iou.detach().clamp(0).type(tobj.dtype)
                 if self.sort_obj_iou:
-                    sort_id = torch.argsort(score_iou)
-                    b, a, gj, gi, score_iou = b[sort_id], a[sort_id], gj[sort_id], gi[sort_id], score_iou[sort_id]
-                tobj[b, a, gj, gi] = (1.0 - self.gr) + self.gr * score_iou  # iou ratio
+                    j = iou.argsort()
+                    b, a, gj, gi, iou = b[j], a[j], gj[j], gi[j], iou[j]
+                if self.gr < 1:
+                    iou = (1.0 - self.gr) + self.gr * iou
+                tobj[b, a, gj, gi] = iou  # iou ratio
 
                 # Classification
                 if self.nc > 1:  # cls loss (only if multiple classes)