Simplify parameter pack handling: use if constexpr to drop extra function

Change-Id: I09b7c4b90d28dc69c9788c645e057762af586879
Reviewed-on: https://gerrit.libreoffice.org/71063
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

sc/source/filter/inc/xestream.hxx

@@ -290,9 +290,9 @@ public:
     void WriteAttributes(sal_Int32 nAttribute, const Str& value, Args... rest)
     {
         WriteAttribute(nAttribute, value);
-        WriteAttributes(rest...);
+        if constexpr(sizeof...(rest) > 0)
+            WriteAttributes(rest...);
     }
-    static void WriteAttributes() {}
 
     sax_fastparser::FSHelperPtr     CreateOutputStream (
                                         const OUString& sFullStream,