I appreciate that the main developers aren't responsible for plugins, but I think this isn't a plugin problem.

Steps to reproduce:  On Windows, enable the latest (2.0.14) Classical Extras plugin and load up the metadata for https://musicbrainz.org/release/afcdc328-cf53-4d01-9593-069078ebd99e

Picard will crash when there are about 5-6 web service calls left to do to load all the CE metadata.

On a Linux build Picard does not crash - I've used https://hub.docker.com/r/mikenye/picard to quickly test on a Debian VM that doesn't have a GUI and the release loaded just fine.

The debug log on Windows doesn't give much away; the last entries are

```

D: 17:19:01,424 webservice._handle_reply:559: Received reply for https://musicbrainz.org/ws/2/work/fa153509-a585-48c9-a788-161074af790b?inc=work-rels+artist-rels+label-rels+place-rels+aliases+tags -> HTTP 200 (OK) D: 17:19:01,425 webservice._handle_reply:572: Response received: {'attributes': [], 'title': 'La vida breve: Acto II. Interludio orquestal', 'aliases': [], 'id': 'fa153509-a585-48c9-a788-161074af790b', 'type-id': None, 'language': None, 'relations': [{'begin': None, 'artist':

{'type': 'Person', 'sort-name': 'Falla, Manuel de', 'disambiguation': 'Spanish composer', 'id': '17268036-f51c-427c-a8a2-241fac69d39f', 'name': 'Manuel de Falla', 'type-id': 'b6e035f4-3ce9-331c-97df-83397230b0df'}

, 'attribute-values': {}, 'type': 'composer', 'target-credit': '', 'end': None, 'attribute-ids': {}, 'direction': 'backward', 'attributes': [], 'ended': False, 'target-type': 'artist', 'source-credit': '', 'type-id': 'd59d99ea-23d4-4a80-b066-edca32ee158f'}, {'attribute-ids': {}, 'target-credit': '', 'type': 'arrangement', 'end': None, 'work': {'attributes': [], 'disambiguation': 'concert piece', 'languages': ['zxx'], 'title': 'Interludio y danza de "La vida breve"', 'type': None, 'iswcs': [], 'id': 'd211fc24-75ae-4c06-978a-27048fa37877', 'type-id': None, 'language': 'zxx'}, 'attribute-values': {}, 'begin': None, 'type-id': '51975ed8-bbfa-486b-9f28-5947f4370299', 'source-credit': '', 'target-type': 'work', 'attributes': [], 'ended': False, 'direction': 'forward'}, {'attribute-values': {}, 'begin': None, 'target-credit': '', 'type': 'parts', 'end': None, 'attribute-ids': {}, 'work': {'id': '098f8cda-64bd-4a7f-a2cc-b46caf37ba84', 'language': None, 'type-id': None, 'iswcs': [], 'type': None, 'languages': [], 'title': 'La vida breve: Acto II', 'disambiguation': '', 'attributes': []}, 'direction': 'backward', 'attributes': [], 'ended': False, 'target-type': 'work', 'source-credit': '', 'type-id': 'ca8d3642-ce5f-49f8-91f2-125d72524e6a'}], 'disambiguation': '', 'languages': [], 'iswcs': [], 'type': None, 'tags': []}

```