Improve error handling for creating autload_psr4.php (joomla#44763)

Author: Hackwar

libraries/namespacemap.php

@@ -145,7 +145,9 @@ protected function writeNamespaceFile($elements)
         $error_reporting = error_reporting(0);
 
         try {
-            File::write($this->file, implode("\n", $content));
+            if (!File::write($this->file, implode("\n", $content))) {
+                throw new Exception('Could not save ' . $this->file, 500);
+            }
         } catch (Exception $e) {
             Log::add('Could not save ' . $this->file, Log::WARNING);