Koreus: fix on broken pages

(cherry picked from commit 12baf681cade7228219964d5b43fa5fc8ca2c3ce)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

share/lua/playlist/koreus.lua

@@ -40,7 +40,9 @@ function parse()
 		end
 		if string.match( line, "<meta name=\"description\"" ) then
 			_,_,description = string.find( line, "content=\"(.-)\"" )
+            if (description ~= nil) then
                 description = vlc.strings.resolve_xml_special_chars( description )
+            end
 		end
 		if string.match( line, "<meta name=\"author\"" ) then
 			_,_,artist = string.find( line, "content=\"(.-)\"" )