[Bug] API return 500 when repository is empty

[6543]

Came Up in https://gitea.com/gitnex/GitNex/issues/154

• Gitea version (or commit ref): 1.9.4 & 1.10.0-rc1
• Can you reproduce the bug at https://try.gitea.io: at gitea.com ...

API call should not return 500 as HTTP status!

query: https://code.obermui.de/api/v1/repos/6543/empty/contents
responce: {"message":"object does not exist [id: master, rel_path: ]","url":"https://code.obermui.de/api/swagger"} + http-code: 500

[lunny]

May related to #8541

[6543]

I dont think so - 1.9.4 has same problem

and #8541 is only merged into master & release/v1.10

[jonasfranz]

Can be reproduced at try.gitea.io: https://try.gitea.io/api/v1/repos/JonasFranzDEV/empty/contents