Deleting files from Media Library when MySQL database locked

[jakubferenc]

While permamently deleting files uploaded to a post, I incidentally had set in the mysql config "innodb_force_recovery = 1" and therefore, as it is my understanding, the database was protected against any changes.

Files were, however, permamently deleted from the filesystem but kept in the databased and show in the media library, naturally without the associated image files.

#25108 was marked as a duplicate.

Return early if postmeta can't be deleted

We're ultimately not doing everything inside of an atomic transaction. So I think I prefer something like 25107.diff​ that specifically waits to see if the primary delete query is successful.

An issue with 25107.diff​ could be, that deleting metadata works, but the primary delete query fails. This results in a post without any meta, like for image sizes, which means, that image_get_intermediate_size() will fail and the image files can't be deleted.

In 26543:

Return false from wp_delete_post() and wp_delete_attachment() if the DELETE is unsuccessful.

This prevents attachments from being deleted off disk when a DB is locked and the delete is otherwise unsuccessful.

fixes #25107.