Some search term return error.

I using the latest version of the plugin, searching for example "dark" I got a error.
Here the log

```
17:18:43.179 T:139885033895680 ERROR: EXCEPTION Thrown (PythonToCppException) : -->Python callback/script returned the following error<--
- NOTE: IGNORING THIS CAN LEAD TO MEMORY LEAKS!
Error Type:
Error Contents: int() argument must be a string or a number, not 'NoneType'
Traceback (most recent call last):
File "/home/mac//.kodi/addons/plugin.video.netflix/addon.py", line 33, in
NAVIGATION.router(paramstring=REQUEST_PARAMS)
File "/home/mac//.kodi/addons/plugin.video.netflix/resources/lib/utils.py", line 60, in wrapped
result = func(*args, **kwargs)
File "/home/mac//.kodi/addons/plugin.video.netflix/resources/lib/Navigation.py", line 265, in router
return self.show_search_results(params.get('term'))
File "/home/mac//.kodi/addons/plugin.video.netflix/resources/lib/utils.py", line 60, in wrapped
result = func(*args, **kwargs)
File "/home/mac//.kodi/addons/plugin.video.netflix/resources/lib/Navigation.py", line 361, in show_search_results
build_url=self.build_url)
File "/home/mac//.kodi/addons/plugin.video.netflix/resources/lib/KodiHelper.py", line 677, in build_search_result_listing
build_url=build_url)
File "/home/mac//.kodi/addons/plugin.video.netflix/resources/lib/KodiHelper.py", line 459, in build_video_listing
params['pin'] = (True, False)[int(video.get('maturity', {}).get('level', 1001)) >= 1000]
TypeError: int() argument must be a string or a number, not 'NoneType'
-->End of Python script error report<--
```

Start with resources/lib/KodiHelper.py at build_video_listing, line 459, and trace the search path from resources/lib/Navigation.py. Reproduce a search for "dark" and inspect how a missing maturity level reaches int(). Done means search results render without the reported TypeError.

Written by the indexing model from the issue text.