help: try topics before commands to avoid "diffs" showing help for diffstat

mercurial/commands.py

@@ -1428,7 +1428,7 b' def help_(ui, name=None, with_version=Fa'
 
     if name and name != 'shortlist':
         i = None
-        for f in (helpcmd, helptopic, helpext):
+        for f in (helptopic, helpcmd, helpext):
             try:
                 f(name)
                 i = None