Fix links in RSS feed

compare https://simplepie.org/demo/?feed=https%3A%2F%2Fwww.openstatsware.org%2Fblog.xml looking at the xml file the links to the image files look ok, e.g. "[www.openstatsware.org/blog/2023-gswe4rp-workshops-wrapup/IMG_0190.JPG](http://www.openstatsware.org/blog/2023-gswe4rp-workshops-wrapup/IMG_0190.JPG)" I don't know why SimplePie is prefixing these further with twice (!) the base URL, e.g. "https://www.openstatsware.org/www.openstatsware.org/www.openstatsware.org/blog/2023-gswe4rp-workshops-wrapup/IMG_0190.JPG" - [ ] make sure that the URLs use "**https**://[www.openstatsware.org](http://www.openstatsware.org/blog/2023-gswe4rp-workshops-wrapup/IMG_0190.JPG)