Can't set a user's quota back to Unlimited #26975

Steps to reproduce

1. Go tu user admin page, set quota to 1GB
2. Once applied, try setting quota back to Unlimited

Expected behaviour

Quota is set back to unlimited

Actual behaviour

Orange error box at the top saying Invalid quota value "none" and refreshing the page shows that the quota wasn't changed.

Server configuration

Operating system:
macOS (I assume this doesn't matter, it works with 9.1.2 on the same setup)

Web server:
nginx

Database:
sqlite

PHP version:
5.6

ownCloud version: (see ownCloud admin page)
master (1f7167a)

Updated from an older ownCloud or fresh install:
fresh

Where did you install ownCloud from:
git + make

Client configuration

Browser:
Safari 10.0.2
Same error in Chrome

Operating system:
macOS 10.12.2