Bootstrap/Load: Only override the $table_prefix global if not already defined.

This aims to provide more flexibility in preloading some environment settings before initializing WordPress.

Follow-up to [18993], [57748].

Props ninos-ego, dd32, swissspidy, SergeyBiryukov.
Fixes #63627.

git-svn-id: https://develop.svn.wordpress.org/trunk@61250 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-settings.php

@@ -140,7 +140,9 @@
  *
  * @global string $table_prefix The database table prefix.
  */
-$GLOBALS['table_prefix'] = $table_prefix;
+if ( ! isset( $GLOBALS['table_prefix'] ) ) {
+	$GLOBALS['table_prefix'] = $table_prefix;
+}
 
 // Set the database table prefix and the format specifiers for database table columns.
 wp_set_wpdb_vars();