hgweb: wrap {files} of changelist entries with mappedgenerator

This also switches the associated templates conditionally, which can't be
a mappinggenerator.

mercurial/hgweb/webutil.py

@@ -509,12 +509,16 b' def changesetentry(web, ctx):'
         archives=web.archivelist(ctx.hex()),
         **pycompat.strkwargs(commonentry(web.repo, ctx)))
 
-def listfilediffs(tmpl, files, node, max):
+def _listfilediffsgen(context, tmpl, files, node, max):
     for f in files[:max]:
         yield tmpl.generate('filedifflink', {'node': hex(node), 'file': f})
     if len(files) > max:
         yield tmpl.generate('fileellipses', {})
 
+def listfilediffs(tmpl, files, node, max):
+    return templateutil.mappedgenerator(_listfilediffsgen,
+                                        args=(tmpl, files, node, max))
+
 def diffs(web, ctx, basectx, files, style, linerange=None,
           lineidprefix=''):