Fixes Pipes/Wires getting blown up when the wall doesn't

Added a check between ex_act on the turf and ex_act on the turf's contents.
If the wall isn't blown out the contents are not blown up.
This is to prevent the annoying behaviour of having pipes and wires getting blown up when the wall on top remains intact (doubling the amount of engineering repair work required.)

Note: If the wall gets blown down to girders ex_act is still applied to the turf's contents.
I could fix this for girders/computers/machines/other solid anchored objects, but that would be getting into feature territory.