Broken urls on help page when GitLab installed under relative URL

Summary

I have GitLab running on official Docker image and served under a relative URL like https://my.domain/gitlab. When I enter the Help page (https://my.domain/gitlab/help) all documents links lack the "/gitlab/" part. I believe it got broke in version 8.14.

Steps to reproduce

Run GitLab under relative URL. Open the Help page. Click on any document link. You land on not existing page.

Expected behavior

Links should open desired pages. e.g. clicking "API" should open https://my.domain/gitlab/help/api/README.md

Actual behavior

Links open non-existing pages (depenging on configuration of your domain). e.g. clicking "API" opens https://my.domain/help/api/README.md

Output of checks

Results of GitLab application Check

Checking GitLab Shell ...

GitLab Shell version >= 4.0.0 ? ... OK (4.0.0)
Repo base directory exists?
default... yes
Repo storage directories are symlinks?
default... no
Repo paths owned by git:git?
default... yes
Repo paths access is drwxrws---?
default... yes
hooks directories in repos are links: ... 
8/1 ... ok
8/6 ... ok
8/7 ... ok
8/8 ... ok
8/9 ... ok
8/10 ... ok
12/11 ... ok
8/12 ... ok
15/13 ... ok
10/14 ... ok
10/15 ... ok
12/16 ... ok
10/18 ... ok
14/19 ... ok
13/20 ... ok
9/21 ... ok
9/22 ... ok
9/23 ... ok
10/24 ... ok
10/25 ... ok
10/26 ... ok
10/27 ... ok
9/28 ... ok
8/29 ... ok
9/30 ... ok
9/34 ... ok
8/35 ... ok
10/36 ... ok
8/37 ... ok
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Access to /var/opt/gitlab/.ssh/authorized_keys: OK
Send ping to redis server: OK
gitlab-shell self-check successful

Checking GitLab Shell ... Finished

Checking Sidekiq ...

Running? ... yes
Number of Sidekiq processes ... 1

Checking Sidekiq ... Finished

Checking Reply by email ...

Reply by email is disabled in config/gitlab.yml

Checking Reply by email ... Finished

Checking LDAP ...

Server: ldapmain
LDAP authentication... Success
LDAP users with access to your GitLab server (only showing the first 100 results)

... HIDDEN LIST OF USRES ...

Checking LDAP ... Finished

Checking GitLab ...

Git configured with autocrlf=input? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config outdated? ... no
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory setup correctly? ... yes
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
projects have namespace: ... 
8/1 ... yes
8/6 ... yes
8/7 ... yes
8/8 ... yes
8/9 ... yes
8/10 ... yes
12/11 ... yes
8/12 ... yes
15/13 ... yes
10/14 ... yes
10/15 ... yes
12/16 ... yes
10/18 ... yes
14/19 ... yes
13/20 ... yes
9/21 ... yes
9/22 ... yes
9/23 ... yes
10/24 ... yes
10/25 ... yes
10/26 ... yes
10/27 ... yes
9/28 ... yes
8/29 ... yes
9/30 ... yes
9/34 ... yes
8/35 ... yes
10/36 ... yes
8/37 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.1.0 ? ... yes (2.3.1)
Your git bin path is "/opt/gitlab/embedded/bin/git"
Git version >= 2.7.3 ? ... yes (2.7.4)
Active users: 36

Checking GitLab ... Finished

Results of GitLab environment info

System information
System:
Current User:   git
Using RVM:      no
Ruby Version:   2.3.1p112
Gem Version:    2.6.6
Bundler Version:1.13.6
Rake Version:   10.5.0
Sidekiq Version:4.2.1

GitLab information
Version:        8.14.1
Revision:       e45bf3d
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
URL:            https://intranet.melog.com/gitlab
HTTP Clone URL: https://intranet.melog.com/gitlab/some-group/some-project.git
SSH Clone URL:  git@repozytorium.melog.com:some-group/some-project.git
Using LDAP:     yes
Using Omniauth: no

GitLab Shell
Version:        4.0.0
Repository storage paths:
- default:      /var/opt/gitlab/git-data/repositories
Hooks:          /opt/gitlab/embedded/service/gitlab-shell/hooks/
Git:            /opt/gitlab/embedded/bin/git