[facet.ctype.char.virtuals] Add missing \pnum

Author: tkoeppe

source/locales.tex

@@ -1839,6 +1839,7 @@
                               char dfault, char* to) const;
 \end{codeblock}
 
+\pnum
 These functions are described identically as those members of the
 same name in the
 \tcode{ctype}