Fixed path of FT in derived conditions

Part of the tests in DD4hep were failing will an error concerning unknown conditions. This was due to "bad" paths for the detector element part of the name, now fixed.

I put bad in quotes, as "FT" did not seem like a bad path, and actually allowed to find the FT detector element, sadly it was hashed as is when reading, while the full DetElem path was used when creating the derived condition (which is "/world/AfterMagnetRegion/T/FT") leading to the problem. LHCb!4184 (merged) introduces a check for such cases with a nicer error message.