Multiple bug fixes

【Contents of the fix】
■Fixed a bug that prevented users from logging in or registering if the permalink setting was set to “post name.
■Fixed a bug that an error occurred when returning from the preview screen, deleting an image, and resetting it.
■Fixed a bug where the string “Private:” was displayed twice in the title of a private post.

【Fixed files】
functions.php
functions/membership/memberpage.php
js/membership-upload.js
single.php
style.cs