Ensure no PHP buffer for SQLite download (#7230)

* Ensure no PHP buffer for SQLite download
fix https://github.com/FreshRSS/FreshRSS/pull/6931#issuecomment-2567037406

* No warning if any case

app/views/importExport/sqlite.phtml

@@ -1,6 +1,7 @@
 <?php
 declare(strict_types=1);
 /** @var FreshRSS_View $this */
+@ob_end_clean();	// Ensure no buffer
 header('Content-Type: application/vnd.sqlite3');
 header('Content-Disposition: attachment; filename="' . basename($this->sqlitePath) . '"');
 header('Cache-Control: private, no-store, max-age=0');