[Filesystem] Check that the directory is writable after created it in dumpFile()

src/Symfony/Component/Filesystem/Filesystem.php

@@ -498,7 +498,9 @@ class Filesystem
 
         if (!is_dir($dir)) {
             $this->mkdir($dir);
-        } elseif (!is_writable($dir)) {
+        }
+
+        if (!is_writable($dir)) {
             throw new IOException(sprintf('Unable to write to the "%s" directory.', $dir), 0, null, $dir);
         }