[cherry-pick] fix mot pose unite deploy cpu mkldnn (#3842)

Author: nemonameless

deploy/python/mot_jde_infer.py

@@ -91,6 +91,8 @@ def __init__(self,
 
     def postprocess(self, pred_dets, pred_embs, threshold):
         online_targets = self.tracker.update(pred_dets, pred_embs)
+        if online_targets == []:
+            return [pred_dets[0][:4]], [pred_dets[0][4]], [1]
         online_tlwhs, online_ids = [], []
         online_scores = []
         for t in online_targets: