gendoc: fix localization of help topic

When a topic provides a callable method for its text, most likely
this text will be generated from different parts, so it does not
make sense to apply gettext on the whole result, rather the method
should provide translation by itself.

This is the case with the extensions topic, which triggers a double
gettext call, making the ASCII codec fail when it encounters 8 bit
characters, and prevents the documentation from being built.

doc/gendoc.py

@@ -103,7 +103,9 b' def show_doc(ui):'
         underlined(gettext(section).upper())
         if callable(doc):
             doc = doc()
-        ui.write(gettext(doc))
+        else:
+            doc = gettext(doc)
+        ui.write(doc)
         ui.write("\n")
 
 if __name__ == "__main__":