geanyminiscript: Don't access private fields

This slightly changes the behavior as it will now follow the setting
from the project open at startup, if any.  It's however probably rather
an improvement, although caching the value is likely not to be a good
idea anyway.

geanyminiscript/src/gms.c

@@ -235,9 +235,11 @@ static void item_activate(GtkMenuItem *menuitem, gpointer gdata)
  */
 void plugin_init(GeanyData *data)
 {
+    const GeanyIndentPrefs *iprefs = editor_get_indent_prefs(NULL);
+
     gms_hnd = gms_new(geany->main_widgets->window,
                     data->interface_prefs->editor_font ,
-                    data->editor_prefs->indentation->width,
+                    iprefs->width,
 					geany->app->configdir
                     ) ;