History display causes page load to stall

If the choice is made to show the radioactivity history on the node form then the page load of the node form either stalls with continual reloads or stops with javascript errors. The problem is caused by the radioactivity-history.js snippet that builds the sparkline graph. There is no protection around this code to stop multiple executions. The first execution on a radioactivity-history div works fine as there is JSON data to process and the graph is created in place of the JSON however subsequent calls no longer find any valid JSON as it is now a graph so there is a javascript error as dataset is NULL. On node form pages with WYSIWYG ajax loads attach behaviors can be called multiple times leading to the JS error and, in my case, continual reload attempts of the page.

The fix is to replace .each(function(match)) with .once('sparkline', function(match)) to avoid multiple processing on each div.