Problem description: If the "percentile line (left)" or "percentile line (right)" is unchecked, the corresponding line is still drawn in the graph preview.

Steps to reproduce:

1. Open any graph
2. Set one of the "Percentile line" checkboxes and enter the corresponding value
3. Open graph preview tab and make sure that the line is drawn
4. Get back to Graph tab and unset the previously set checkbox
5. Open graph preview tab once again
   Result 1: The percentile line is still drawn on the graph preview.
6. Go back to the graph configuration form set the percentile checkboxes and unset the "Show legend" checkbox.
7. Open graph preview tab
   Result 2: The percentile line is not visible anymore even though the corresponding setting is set.

Expected: The percentile line should not be drawn if the corresponding "Percentile line" checkbox is unset, and, since itš a separate setting, the display of this line should not depend on whether the legend is present or not

Example: