Avoid translating empty plugin headers

[Chouby]

WPCS recommends not to translate empty strings. On the other hand, plugin headers may not all be filled, but since #19597, _get_plugin_data_markup_translate() translates them all whether they are empty or not.

I propose to check that the string is not empty before attempting to translate it.

[johnbillion]

@Chouby Could you provide an example of a plugin header that results in empty strings being translated? Thanks!

[Chouby]

There are quite many, generally due to empty AuthorURI or PluginURI. Here are a few examples:

• ​https://plugins.trac.wordpress.org/browser/gutenberg/tags/12.4.1/gutenberg.php
• ​https://plugins.trac.wordpress.org/browser/the-events-calendar/tags/5.12.4/the-events-calendar.php
• ​https://plugins.trac.wordpress.org/browser/wp-all-import/tags/3.6.5/plugin.php

Trac ticket: https://core.trac.wordpress.org/ticket/54586

[audrasjb]

Looks good to me. I added a PR to run the unit tests, and then it should be good to go.

[audrasjb]

In 53181:

Plugins: Avoid translating empty plugin headers.

This change aims to avoid unnecessarily translating empty strings from plugin headers, by removing empty fields from translation process in _get_plugin_data_markup_translate().

Props Chouby, johnbillion, audrasjb.
Fixes #54586.

committed in https://core.trac.wordpress.org/changeset/53181