templatekw: do not directly call .gen

mercurial/templatekw.py

@@ -613,10 +613,7 b' def showsuccessorssets(context, mapping)'
 
     # Format the successorssets
     def render(d):
-        t = []
-        for i in d.gen():
-            t.append(i)
-        return "".join(t)
+        return templateutil.stringify(context, mapping, d)
 
     def gen(data):
         yield "; ".join(render(d) for d in data)