Space is double-escaped when submitting custom shorturl keyword

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Version

1.9.2

Description

When using a simple custom plugin such as shown in #3694 to allow (%20) in shorturl keywords, it is still not possible to create a custom keyword containing via the admin panel.

As submitted to the admin-ajax.php endpoint, the custom keyword (e.g. some space) appears to be double-escaped as some%2520space in the parameters sent. This leads the backend to create a shorturl with the incorrect keyword some20space.

Expectation

The frontend should only escape the keyword parameter containing a space once (some%20space), and the backend should then create the keyword some space (assuming that has been added to the shorturl charset by a plugin).

Reproduction steps

No response

Context

No response

Start by tracing custom keyword submission through the admin panel to the admin-ajax.php endpoint, using the double-escaped value described in the issue. Check where the keyword is escaped on the frontend and decoded by the backend. Done means a keyword such as some space is sent once as some%20space and is created as some space when a plugin permits spaces.