Files embedded in booking form do not work

If the teacher embeds a file in the "Booking instructions" for the booking form, then links to that file are displayed incorrectly.

Debugging info:

Before calling format_text(), the content must be processed with file_rewrite_pluginfile_urls()

• line 1326 of /lib/weblib.php: call to debugging()
• line 1007 of /mod/scheduler/renderer.php: call to format_text()
• line 401 of /lib/outputrenderers.php: call to mod_scheduler_renderer->render_scheduler_appointment_info()
• line 148 of /mod/scheduler/studentview.controller.php: call to plugin_renderer_base->render()
• line 48 of /mod/scheduler/studentview.php: call to include()
• line 71 of /mod/scheduler/view.php: call to include()