Set `MPD is not running` in mpdarc-widget current song when MPD is not running.

mpdarc-widget/mpdarc.lua

@@ -70,10 +70,14 @@ local update_graphic = function(widget, stdout, _, _, _)
       mpdarc_current_song_widget.markup = current_song
     else
       icon.image = STOP_ICON_NAME
+      if string.len(stdout) == 0 then -- MPD is not running
+        mpdarc_current_song_widget.markup = "MPD is not running"
+      else
         widget.colors = { beautiful.widget_red }
         mpdarc_current_song_widget.markup = ""
       end
     end
+end
 
 mpdarc:connect_signal("button::press", function(_, _, _, button)
     if (button == 1) then awful.spawn(TOGGLE_MPD_CMD, false)      -- left click