Fix a markup error: do not omit a method's parameter list if it is

empty.

Doc/lib/liburllib2.tex

@@ -560,6 +560,6 @@ Open the gopher resource indicated by \var{req}.
 
 \subsection{UnknownHandler Objects \label{unknown-handler-objects}}
 
-\begin{methoddesc}[UnknownHandler]{unknown_open}
+\begin{methoddesc}[UnknownHandler]{unknown_open}{}
 Raise a \exception{URLError} exception.
 \end{methoddesc}