If a users saves the project settings page the repository size limit will be removed

Summary

If a user is saving anything in the project settings page it overrides repository size limit for this repository with an empty string.
That means the repository size limit is overwritten and lost.

Steps to reproduce

• Set repository size limit to 1024MB by an administrator.
• As a user with Master permission in that repository change the description of the Repo

What is the current bug behavior?

• Repository will end up with empty MB as repository limit

What is the expected correct behavior?

• Repository should keep size limit set by administrator

Output of checks

Results of GitLab environment info

System information
System:
Proxy:          no
Current User:   git
Using RVM:      no
Ruby Version:   2.3.3p222
Gem Version:    2.6.6
Bundler Version:1.13.7
Rake Version:   10.5.0
Redis Version:  3.2.5
Git Version:    2.10.2
Sidekiq Version:4.2.7

GitLab information
Version:        9.0.2-ee
Revision:       3ed6218
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
DB Version:     9.6.1
URL:            https://internal.domain.de
HTTP Clone URL: https://internal.domain.de/some-group/some-project.git
SSH Clone URL:  git@internal.domain.de:some-group/some-project.git
Elasticsearch:  no
Geo:            no
Using LDAP:     yes
Using Omniauth: no

GitLab Shell
Version:        5.0.0
Repository storage paths:
- default:      /var/opt/gitlab/git-data/repositories
Hooks:          /opt/gitlab/embedded/service/gitlab-shell/hooks/
Git:            /opt/gitlab/embedded/bin/git

Results of GitLab application Check

All tests are successful!