don't add default compressors two times if disabled

don't add default compressors two times if disabled

This is in so far pointless as the first match will deal with the
extension, so we don't actually ever use these second instances –
probably for the better as most need arguments to behave as epected &
more importantly: the point of the exercise disabling their use for
testing proposes.

Gbp-Dch: Ignore