--save-txt bug fix (#763)

test.py

@@ -128,11 +128,11 @@ def test(data,
             # Append to text file
             if save_txt:
                 gn = torch.tensor(shapes[si][0])[[1, 0, 1, 0]]  # normalization gain whwh
-                txt_path = str(out / Path(paths[si]).stem)
-                pred[:, :4] = scale_coords(img[si].shape[1:], pred[:, :4], shapes[si][0], shapes[si][1])  # to original
-                for *xyxy, conf, cls in pred:
+                x = pred.clone()
+                x[:, :4] = scale_coords(img[si].shape[1:], x[:, :4], shapes[si][0], shapes[si][1])  # to original
+                for *xyxy, conf, cls in x:
                     xywh = (xyxy2xywh(torch.tensor(xyxy).view(1, 4)) / gn).view(-1).tolist()  # normalized xywh
-                    with open(txt_path + '.txt', 'a') as f:
+                    with open(str(out / Path(paths[si]).stem) + '.txt', 'a') as f:
                         f.write(('%g ' * 5 + '\n') % (cls, *xywh))  # label format
 
             # Clip boxes to image bounds