api request for issue always returns nil for milestone

[ghost]

• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)

example url: https://try.gitea.io/api/v1/repos/nexustrap/issue_missing_milestone_api_v1/issues/1?access_token=dc52cb4688603549d465e10ffa0b371b05489ada

Description

Create an repository, issue and milestone on try.gitea.io.
Assign the milestone to the newly created issue.

curl -X GET "https://try.gitea.io/api/v1/repos/nexustrap/issue_missing_milestone_api_v1/issues/1?access_token=dc52cb4688603549d465e10ffa0b371b05489ada" -H "accept: application/json"

The resulting json shows milestone = 'nil'

Screenshots

[sankethpb]

@lafriks Is there any workaround for this in 1.7.2?
Would be great to have it back ported to 1.7.3, thank you.