Fix case with no user

lib/private/Share20/Manager.php

@@ -1212,6 +1212,10 @@ class Manager implements IManager {
 	 * @return bool
 	 */
 	public function sharingDisabledForUser($userId) {
+		if ($userId === null) {
+			return false;
+		}
+
 		if (isset($this->sharingDisabledForUsersCache[$userId])) {
 			return $this->sharingDisabledForUsersCache[$userId];
 		}

lib/public/Util.php

@@ -181,7 +181,12 @@ class Util {
 			self::$shareManager = \OC::$server->getShareManager();
 		}
 
-		return self::$shareManager->sharingDisabledForUser(\OC::$server->getUserSession()->getUser()->getUID());
+		$user = \OC::$server->getUserSession()->getUser();
+		if ($user !== null) {
+			$user = $user->getUID();
+		}
+
+		return self::$shareManager->sharingDisabledForUser($user);
 	}
 
 	/**