Issue Summary

A query which returns a datetime column, a column with a finite set of text values used for the y axis and with the y axis scale set to 'Category' shows all values on the x axis (y has only the label '0')

Steps to Reproduce

1. Have a query with a datetime column and at least a second column with a limit number of text values
2. Create a new Chart > Scatter visualization with datetime as the x axis and the other column as y axis, set the scale of the y axis to 'Category'.

Expected: Data points distributed across different category values. At the moment the y axis only has '0'

Technical details:

• Redash Version: 6.0.0-dev (was working in an earlier version, ask Mozilla data engineers which version they ran on 2018-10-26)
• Browser/OS: Firefox 65.0a1
• How did you install Redash: Mozilla did