pypi, retry when receiving a 200 with empty body

For some reason, pypi is returning a 200 and an empty body from
time to time. The next time you query the same endpoint it
returns a proper JSON object. This is not fixing a bug in
poetry, but working around the issue.

poetry/repositories/pypi_repository.py

@@ -324,6 +324,9 @@ def _get_release_info(self, name: str, version: str) -> dict:
     def _get(self, endpoint: str) -> Union[dict, None]:
         try:
             json_response = self.session.get(self._base_url + endpoint)
+            if json_response.status_code == 200 and json_response.content == b"":
+                logger.warn("Got empty response from PyPI for %s. Retrying...", endpoint)
+                json_response = self.session.get(self._base_url + endpoint)
         except requests.exceptions.TooManyRedirects:
             # Cache control redirect loop.
             # We try to remove the cache and try again