fix TprAtFpr metrics

ppcls/metric/metrics.py

@@ -204,8 +204,10 @@ class TprAtFpr(nn.Layer):
                 gt_pos_score_list > threshold) / len(gt_pos_score_list)
             if len(gt_neg_score_list) == 0 and tpr > max_tpr:
                 max_tpr = tpr
-                result = "threshold: {}, fpr: {}, tpr: {:.5f}".format(
-                    threshold, fpr, tpr)
+                result = "threshold: {}, fpr: 0.0, tpr: {:.5f}".format(
+                    threshold, tpr)
+                msg = f"The number of negative samples is 0, please add negative samples."
+                logger.warning(msg)
             fpr = np.sum(
                 gt_neg_score_list > threshold) / len(gt_neg_score_list)
             if fpr <= self.max_fpr and tpr > max_tpr: