MDL-83293 core: Fix path separator when guessing the base path

Ensure that path separator for the script when guessing the base path
uses forward slash instead of the OS' directory separator.
(e.g. "\" in Windows)

lib/classes/router.php

@@ -92,14 +92,17 @@ protected function guess_basepath(): string {
  // Moodle is not guaranteed to exist at the domain root.
  // Strip out the current script.
  $scriptroot = parse_url($CFG->wwwroot, PHP_URL_PATH);
+ $scriptfile = str_replace(
+ realpath($CFG->dirroot),
+ '',
+ realpath($_SERVER['SCRIPT_FILENAME']),
+ );
+ // Replace occurrences of backslashes with forward slashes, especially on Windows.
+ $scriptfile = str_replace('\\', '/', $scriptfile);
  $relativeroot = sprintf(
  '%s%s',
  $scriptroot,
- str_replace(
- realpath($CFG->dirroot),
- '',
- realpath($_SERVER['SCRIPT_FILENAME']),
- ),
+ $scriptfile,
  );
 
  // The server is not configured to rewrite unknown requests to automatically use the router.