Empty response for existing (old) plugin version

[amvanbaren]

Fixes #431

Added RegistryAPITest.testGetQueryExtensionVersion to replicate the issue.

Manual testing steps

• Download https://open-vsx.org/api/ms-python/python/2022.0.1814523869/file/ms-python.python-2022.0.1814523869.vsix.
• Download https://open-vsx.org/api/ms-python/python/2020.8.105369/file/ms-python.python-2020.8.105369.vsix.
• Create namespace ms-python.
• Publish the two downloaded extensions.
• Execute query: curl --location --request GET 'http://localhost:8080/api/-/query?extensionId=ms-python.python&extensionVersion=2020.8.105369'
• Expected result: a response containing ms-python.python version 2020.8.105369.