fix loss of a space after indexing markup

Doc/lib/libhtmllib.tex

@@ -20,7 +20,7 @@ from and extends the \class{SGMLParser} class defined in module
 \refmodule{sgmllib}\refstmodindex{sgmllib}.  The \class{HTMLParser}
 implementation supports the HTML 2.0 language as described in
 \rfc{1866}.  Two implementations of formatter objects are provided in
-the \refmodule{formatter}\refstmodindex{formatter} module; refer to the
+the \refmodule{formatter}\refstmodindex{formatter}\ module; refer to the
 documentation for that module for information on the formatter
 interface.
 \withsubitem{(in module sgmllib)}{\ttindex{SGMLParser}}