hgweb: wrap {succsandmarkers} with mappinggenerator

This is also a generator of mappings, which needs a wrapper.

mercurial/hgweb/webutil.py

@@ -378,7 +378,7 b' def linerange(req):'
 def formatlinerange(fromline, toline):
     return '%d:%d' % (fromline + 1, toline)
 
-def succsandmarkers(context, mapping):
+def _succsandmarkersgen(context, mapping):
     repo = context.resource(mapping, 'repo')
     itemmappings = templatekw.showsuccsandmarkers(context, mapping)
     for item in itemmappings.tovalue(context, mapping):
@@ -386,6 +386,9 b' def succsandmarkers(context, mapping):'
                                        for successor in item['successors'])
         yield item
 
+def succsandmarkers(context, mapping):
+    return templateutil.mappinggenerator(_succsandmarkersgen, args=(mapping,))
+
 # teach templater succsandmarkers is switched to (context, mapping) API
 succsandmarkers._requires = {'repo', 'ctx'}