test: fix StopIteration exception in p2p_node_network_limited.py

The `next()` call throws an exception if the default parameter is omitted and the iterator is exhausted.
Fix it by providing a default value.

The failure can be tested by commenting out lines 90 and 91 in the test (the `self.connect_nodes(2, 0)``).
Since there is no connection, the node in question retrieves a single element in the 'getchaintips()' call.
This scenario without the fix, aborts the test right away, throwing an StopIteration exception, and with
the fix, the test properly waits until the timeout (wait_until() call).

test/functional/p2p_node_network_limited.py

@@ -92,7 +92,8 @@ def test_avoid_requesting_historical_blocks(self):
 
         # Wait until the full_node is headers-wise sync
         best_block_hash = pruned_node.getbestblockhash()
-        self.wait_until(lambda: next(filter(lambda x: x['hash'] == best_block_hash, full_node.getchaintips()))['status'] == "headers-only")
+        default_value = {'status': ''}  # No status
+        self.wait_until(lambda: next(filter(lambda x: x['hash'] == best_block_hash, full_node.getchaintips()), default_value)['status'] == "headers-only")
 
         # Now, since the node aims to download a window of 1024 blocks,
         # ensure it requests the blocks below the threshold only (with a