Issue description is not taken atwho selection in consideration

Summary

Clicking on at who dropdown is not taken in consideration when editing an issue.

Steps to reproduce

1. click on edit
2. type @ and the initial letter of the name
3. choose the person on the dropdown
4. save
5. issue is updated with only the thing I typed, not the thing I choose on the dropdown

Relevant logs and/or screenshots

assigned to @iamphill

This is pretty big. We should put this into %9.3 patch release.

Wdyt @jschatz1

@filipa @ClemMakesApps This seems like a inline edit spam issue. See https://gitlab.com/gitlab-org/gitlab-ce/issues/29483

cc @stanhu

@MadLittleMods its nothing to do with spam, its a bug.

Created this in ee