TrigHitDVHypoAlg: fix uninitialized variables

Frank Winklmeierrequested to merge
fwinkl/athena:fwinkl_20241211T165518 into 24.0

Note that m_useBeamSpot is nowhere set and thus the behavior whether the beamspot is used or not was undefined.

Fixes cppcheck warnings in !76498 (closed).

Edited by Frank Winklmeier

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