Placeholder names should not use user input

My views crosstab query just broke, and it turned out to be because my field values started to contain colons. You're using the field values in the placeholder names, so the SQL execution breaks if a placeholder contains arbitrary colons.

There is no need to use the field value (i.e. arbitrary user input) to generate placeholder names. And while I was bouncing around some code to see "what would Views do", I found a placeholder() method that is made for this.

So... this is an easy one fix (because your code already does everything right, besides the placeholder name).