fix: Avoid segfault in track conversion

[benjaminhuth]

For some rare cases it can be the case that no reference surface is present...

[codecov]

Codecov Report

Merging #2437 (5ef5ea2) into main (af4ad67) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2437   +/-   ##
=======================================
  Coverage   49.70%   49.70%           
=======================================
  Files         458      458           
  Lines       25949    25949           
  Branches    11919    11919           
=======================================
  Hits        12899    12899           
  Misses       4596     4596           
  Partials     8454     8454           

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[github-actions]

📊: Physics performance monitoring for 5ef5ea2

Full contents

physmon summary

• ✅ CKF truth_smeared
• ✅ IVF truth_smeared
• ✅ AMVF truth_smeared
• ✅ Track Summary CKF truth_smeared
• ✅ Seeding truth_estimated
• ✅ CKF truth_estimated
• ✅ IVF truth_estimated
• ✅ AMVF truth_estimated
• ✅ Track Summary CKF truth_estimated
• ✅ Seeding seeded
• ✅ CKF seeded
• ✅ IVF seeded
• ✅ AMVF seeded
• ✅ AMVF (+grid seeder) seeded
• ✅ Track Summary CKF seeded
• ✅ Seeding orthogonal
• ✅ CKF orthogonal
• ✅ IVF orthogonal
• ✅ AMVF orthogonal
• ✅ Track Summary CKF orthogonal
• ✅ Ambisolver seeded
• ✅ Ambisolver orthogonal
• ✅ Seeding ttbar
• ✅ CKF ttbar
• ✅ Ambisolver
• ✅ AMVF ttbar
• ✅ AMVF (+grid seeder) ttbar
• ✅ Truth tracking (GSF)
• ✅ Truth tracking
• ✅ Particles inital fatras
• ✅ Particles final fatras
• ✅ Particles inital geant4
• ✅ Particles final geant4

Invalidated by push of 5ef5ea2