fix: Fix trailing slash in media urls returned from heresphere api

[Yoooi0]

When using the /heresphere api the media urls are returned with a trailing slash:

http://localhost:9999/api/dms/file/1/
http://localhost:9999/api/dms/file/1/?dnt=true

This PR fixes it to:

http://localhost:9999/api/dms/file/1
http://localhost:9999/api/dms/file/1?dnt=true

Which also matches the /deovr api:

xbvr/pkg/api/deovr.go

Line 402 in 9f253fe

URL: fmt.Sprintf("%v/api/dms/file/%v/%v%v", session.DeoRequestHost, file.ID, scene.GetFunscriptTitle(), dnt),

Blame #969