PaymentBackend: skip poll faster if there is no transaction (#66487)

combo/apps/lingo/models.py

@@ -257,6 +257,9 @@ class PaymentBackend(models.Model):
             status__in=Transaction.RUNNING_STATUSES,
         ).order_by('pk')
         last_pk = -1
+        # skip fast in order to save some resources on database
+        if not transactions.exists():
+            return
         while True:
             # lock each transaction before trying to poll it
             with atomic():