Work item comments can be submitted twice using keyboard

Summary

Using cmd-enter more than once in succession will result in multiple comments being added.

Steps to reproduce

  1. Open a work item such as a task or epic (on gitlab-org)
  2. Write a comment
  3. Use cmd+enter quickly 2+ times to submit

Example Project

gitlab-org

What is the current bug behavior?

Creates >1 comment

What is the expected correct behavior?

Creates 1 comment

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info 

(For installations with omnibus-gitlab package run and paste the output of: \`sudo gitlab-rake gitlab:env:info\`) (For installations from source run and paste the output of: \`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production\`)

Results of GitLab application Check

Expand for output related to the GitLab application check 

(For installations with omnibus-gitlab package run and paste the output of: `sudo gitlab-rake gitlab:check SANITIZE=true`)

(For installations from source run and paste the output of: `sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true`)

(we will only investigate if the tests are passing)

Possible fixes