Fix shownotes for episodes that contain HTML comments.

When html5lib is used, a function is returned for each comment in the
HTML. It should be safe to skip functions until something else is found
to use them that causes issues finding hyperlinks.

Fixes #1195.

src/gpodder/util.py

@@ -776,6 +776,10 @@ class ExtractHyperlinkedText(object):
         return self.extracter.get_result()
 
     def visit(self, element):
+        # skip functions generated by html5lib for comments in the HTML
+        if callable(element.tag):
+            return
+
         NS = '{http://www.w3.org/1999/xhtml}'
         tag_name = (element.tag[len(NS):] if element.tag.startswith(NS) else element.tag).lower()
         self.extracter.handle_starttag(tag_name, list(element.items()))