Xml_node: skip leading whitespace in with_raw_node

This patch makes the 'with_raw_node' method more useful in situations
where content of an Xml_node is fed into an Xml_generator, i.e., the
rules report/rom mechanism of the window layouter.

repos/base/include/util/xml_node.h

@@ -760,7 +760,8 @@ class Genode::Xml_node
 		template <typename FN>
 		void with_raw_node(FN const &fn) const
 		{
-			fn(_addr, _tags.end.next_token().start() - _addr);
+			char const *start_ptr = _tags.start.token().start();
+			fn(start_ptr, _tags.end.next_token().start() - start_ptr);
 		}
 
 		/**