Issue Board Lists movement offset

Summary

Moving a Issue Board list to the last movable position moves it less than indicated.

Using drag-n-drop shows the list moved to the correct place:

When the page is refreshed the list is offset by one position:

Steps to reproduce

Within a project

• Generate default issue board lists
• Move the first or second movable lists to the last position
• Refresh the page

Expected behavior

The moved list still in the same position after a page refresh.

Actual behavior

The moved list position is offset by one upon refreshing the page.

Output of checks

Results of GitLab application Check

Checking GitLab Shell ...

GitLab Shell version >= 3.6.3 ? ... OK (3.6.3)
Repo base directory exists?
default... yes
Repo storage directories are symlinks?
default... no
Repo paths owned by runner:runner?
default... yes
Repo paths access is drwxrws---?
default... yes
hooks directories in repos are links: ... 
2/1 ... ok
3/2 ... ok
3/3 ... ok
3/4 ... ok
3/5 ... ok
4/6 ... ok
4/7 ... ok
5/8 ... ok
Running /home/runner/projects/gitlab-development-kit/gitlab-shell/bin/check
Check GitLab API access: OK
Access to /home/runner/projects/gitlab-development-kit/.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 ...

LDAP is disabled in config/gitlab.yml

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GitLab config outdated?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? ... no
  Try fixing it:
  Install the init script
  For more information see:
  doc/install/installation.md in section "Install Init Script"
  Please fix the error above and rerun the checks.
Init script up-to-date? ... can't check because of previous errors
projects have namespace: ... 
2/1 ... yes
3/2 ... yes
3/3 ... yes
3/4 ... yes
3/5 ... yes
4/6 ... yes
4/7 ... yes
5/8 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.1.0 ? ... yes (2.3.1)
Your git bin path is "/usr/bin/git"
Git version >= 2.7.3 ? ... yes (2.10.0)
Active users: 26

Checking GitLab ... Finished

Results of GitLab environment info

System information
System:		
Current User:	runner
Using RVM:	yes
RVM Version:	1.27.0
Ruby Version:	2.3.1p112
Gem Version:	2.5.1
Bundler Version:1.13.1
Rake Version:	10.5.0
Sidekiq Version:4.2.1

GitLab information
Version:	8.13.0-pre
Revision:	90462cb
Directory:	/home/runner/projects/gitlab-development-kit/gitlab
DB Adapter:	postgresql
URL:		http://localhost:3000
HTTP Clone URL:	http://localhost:3000/some-group/some-project.git
SSH Clone URL:	ssh://runner@localhost:2222/some-group/some-project.git
Using LDAP:	no
Using Omniauth:	no

GitLab Shell
Version:	3.6.3
Repository storage paths:
- default: 	/home/runner/projects/gitlab-development-kit/repositories/
Hooks:		/home/runner/projects/gitlab-development-kit/gitlab-shell/hooks/
Git:		/usr/bin/git

Possible fixes

Currently the list positions start from 0, but this position is always occupied by the backlog list.

Then when a list is moved it is always moved one position less than desired.

Changing the position start and limits in those files restores the correct behavior:

boards_store.js

lists/move_service.rb