Always apply wp_sqlite_default_db_name filter to DB_NAME

[sejas]

• Related to Upgrade SQLite database integration plugin to fix preview sites Automattic/studio#1839

This PR applies the wp_sqlite_default_db_name filter in all cases, even if DB_NAME was defined, so we can override the database name, and fix the behaviour in remote servers where DB_NAME is already defined.

Testing instructions:

Warning

These steps are not currently working, but they represent the desired behavior.

• Break your database connection:
  • Go to your wp-config.php
  • Copy the value of your DB_NAME
  • Change it to any value to break your database connection
  • Access the homepage of your site and observe the error: Error establishing a database connection
• Fix your database connection using the filter:
  • Create a new mu-plugin with the code below these instructions.
  • Access your homepage
  • Observe the site loads correctly

<?php

add_filter( 'wp_sqlite_default_db_name', function( $db_name ) {
	return 'database_name_here'; // Or any other value that you copied from your wp-config.php
} );

[sejas]

@JanJakes, I've created this PR trying to override the DB_NAME when we don't have control over that variable, however the filter is not working. Do you know how should I define the filter?
If the wp-includes/sqlite/db.php file loads before any plugin, why do we have a filter in the first place?

[sejas]

• Closing in favor of Add WP_SQLITE_DB_NAME constant to take precedence over DB_NAME #261

[JanJakes]

@sejas Thanks for looking into this!

Closing in favor of #261

Yeah, good call. This filter is not meant to be used that way and will likely be removed.