gauges with min=max limits do not render

Hi everyone,

first of all, I would like to thank you for this fantastic piece of software. Much appreciated!

While building a dashboard I erroneously assigned min and max parameters for a Gauge the same value. No error was shown and Firefox complained with "This page is slowing your browser down. Do you want to stop it or keep waiting?" and I had no clue where this came from. I think it would be helpful to check for this case and show an error.