composer: dont execute anything with active `sudo session`

its common that an update of composer happens with sudo, as composer is installed in a place which is only changeable with higher privileges.

Its not uncommon, that an self-update is made directly before an install/updaten command. To avoid easy privilege escalation in case of an evil attack (like a worm spreading trough the composer ecosystem) we should add a check for an active sudo session, and block further execution if found.

Such malware could spread silently as sudo allows sudo -n true which allows for testing for an active session, without triggering the typical interactive password input.