Bootstrap/Load: Check $_SERVER['SCRIPT_NAME'] exists before passing…

… to `strpos()` in `wp_fix_server_vars()`.

If `SCRIPT_NAME'` does not exist (which can happen in cron jobs), the following happens:

* PHP 8.1+:
    * `Warning: Undefined array key "SCRIPT_NAME"`
    * `Deprecated: strpos(): Passing null to parameter #1 ($haystack) of type string is deprecated` 
* PHP 8.0: `Warning: Undefined array key "SCRIPT_NAME"`
* PHP 5.6-7.4: No warning or notice

This commit checks if the key exists before passing it to `strpos()`. This resolves the warning, notice, and future error.

Follow-up to [3034], [3069], [12732].

Props audrasjb, costdev, hellofromTonya, karpstrucking, mcjambi, sergeybiryukov.
Fixes #54142.

git-svn-id: https://develop.svn.wordpress.org/trunk@52144 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/load.php

@@ -76,7 +76,7 @@ function wp_fix_server_vars() {
 	}
 
 	// Fix for Dreamhost and other PHP as CGI hosts.
-	if ( strpos( $_SERVER['SCRIPT_NAME'], 'php.cgi' ) !== false ) {
+	if ( isset( $_SERVER['SCRIPT_NAME'] ) && ( strpos( $_SERVER['SCRIPT_NAME'], 'php.cgi' ) !== false ) ) {
 		unset( $_SERVER['PATH_INFO'] );
 	}