Add extra check so we don't error out on type
Add extra check so we don't error out on type

json_decode can return false if we have invalid data.
In that case just assume there was nothing cached

Signed-off-by: Roeland Jago Douma <982d370f7dc34a05b4abe8788f899578d515262d@famdouma.nl>

andreas-p/nextcloud-server,andreas-p/nextcloud-server,nextcloud/server,nextcloud/server,michaelletzgus/nextcloud-server,andreas-p/nextcloud-server,andreas-p/nextcloud-server,michaelletzgus/nextcloud-server,michaelletzgus/nextcloud-server,nextcloud/server,andreas-p/nextcloud-server,michaelletzgus/nextcloud-server,nextcloud/server