Fix size calculation caused by 7c2e79ae (bug #13998)

The commit missed adjusting `size', as done previously, which is used as
an argument to pulseaudio_button_set_size.

Signed-off-by: Sean Davis <smd.seandavis@gmail.com>

panel-plugin/pulseaudio-plugin.c

@@ -254,11 +254,13 @@ pulseaudio_plugin_size_changed (XfcePanelPlugin *plugin,
   gint              icon_size;
 
   /* The plugin only occupies a single row */
+  size /= xfce_panel_plugin_get_nrows(plugin);
+
 #if LIBXFCE4PANEL_CHECK_VERSION (4, 13, 0)
   icon_size = xfce_panel_plugin_get_icon_size (plugin);
 #else
   // fall-back for older panel versions
-  icon_size = size / xfce_panel_plugin_get_nrows(plugin);
+  icon_size = size;
   icon_size -= 4;
   if (icon_size < 24)
     icon_size = 16;