The get_circuit_slots method of DebugEndpoint should handle the case when tunnel_community is None

[kozlovsky]

The run method of RESTComponent has the following lines:

torrent_checker = None if config.gui_test_mode else torrent_checker_component.torrent_checker
tunnel_community = None if config.gui_test_mode else tunnel_component.community
gigachannel_manager = None if config.gui_test_mode else gigachannel_manager_component.gigachannel_manager

That is, tunnel_community is None when Tribler is started for GUI tests.

At the same time, the DebugEndpoint in the RESTComponent.run method is initialized in the following way:

self.maybe_add('/debug', DebugEndpoint, config.state_dir, log_dir,
               tunnel_community=tunnel_community,
               resource_monitor=resource_monitor_component.resource_monitor,
               core_exception_handler=self._core_exception_handler)

Here, tunnel_community is passed as None when Tribler is in gui_test_mode.

The maybe_add method does not affect this situation, as it only handles special NoneComponent arguments and not normal None values.

Therefore, the code of DebugEndpoint should expect to handle the situation gracefully when the tunnel_community is None. But in the get_circuit_slots method, it currently expects a non-None instance of tunnel_community.

This PR fixes the problem by handling the case when self.tunnel_community is None in DebugEndpoint

[drew2a]

Related to #7495