BUGFIX: check if there is any value, not the value itself

Otherwise if the quota usage is 0, it will evaluate to `False` and there will be an exception when trying to assign 

```python
data.append({"x": int(time.mktime(parser.parse(date_getter(row)).timetuple())),
             "y": y * gb,
             "limit": limit * gb})
```

#EDIT 
Also added quota limit red line to the quota charts