Send cookie FreshRSS_login only once

Prior to this patch, two cookies with the same name were sent, the first
one was to destroy the cookie, and the second one to create it

app/Models/Auth.php

@@ -236,8 +236,8 @@ class FreshRSS_FormAuth {
 
 	public static function deleteCookie() {
 		$token = Minz_Session::getLongTermCookie('FreshRSS_login');
-		Minz_Session::deleteLongTermCookie('FreshRSS_login');
 		if (ctype_alnum($token)) {
+			Minz_Session::deleteLongTermCookie('FreshRSS_login');
 			@unlink(DATA_PATH . '/tokens/' . $token . '.txt');
 		}