Don't cache status_config.php when it's not populated

When the dynamic css file `status_config.php` can't be generated, force
a no-caching header to avoid the client caching a wrong version of this
file.

Fixes #24189

css/status_config.php

@@ -75,6 +75,7 @@
 
 if( $t_referer_page == auth_login_page() ) {
 	# custom status colors not needed.
+	http_caching_headers( false );
 	exit;
 }
 
@@ -86,6 +87,7 @@
 	case 'account_update.php':
 		# We don't need custom status colors on login page, and this is
 		# actually causing an error since we're not authenticated yet.
+		http_caching_headers( false );
 		exit;
 }