Fix getting db size for sqlite

See https://github.com/FreshRSS/FreshRSS/issues/729

app/Models/EntryDAOSQLite.php

@@ -169,6 +169,6 @@ class FreshRSS_EntryDAOSQLite extends FreshRSS_EntryDAO {
 	}
 
 	public function size($all = false) {
-		return @filesize(DATA_PATH . '/' . $this->current_user . '.sqlite');
+		return @filesize(join_path(DATA_PATH, 'users', $this->current_user, 'db.sqlite'));
 	}
 }