Web.poll_feed_task: tighten last_polled_feed check to only if the task param is greater

for #1712

tests/test_web.py

@@ -2493,7 +2493,7 @@ class WebTest(TestCase):
 
         got = self.post('/queue/poll-feed', data={
             'domain': 'user.com',
-            'last_polled': (NOW + timedelta(minutes=1)).isoformat(),
+            'last_polled': (NOW - timedelta(minutes=1)).isoformat(),
         })
         self.assertEqual(204, got.status_code)
         self.assertEqual(NOW, self.user.key.get().last_polled_feed)

web.py

@@ -883,7 +883,7 @@ def poll_feed_task():
     logger.info(f'Last poll: {user.last_polled_feed}')
     last_polled = request.form.get('last_polled')
     if (last_polled and user.last_polled_feed
-            and last_polled != user.last_polled_feed.isoformat()):
+            and last_polled < user.last_polled_feed.isoformat()):
         logger.warning('duplicate poll feed task! deferring to other task')
         return '', 204