[ALICE3] Fix initialization of 3prong fitter in a3 multicharm finder

[jesgum]

No description provided.

[github-actions]

O2 linter results: ❌ 0 errors, ⚠️ 0 warnings, 🔕 0 disabled

[alibuild]

Auto-approving on behalf of @jesgum.

[alibuild]

Error while checking build/O2Physics/code-check for 5ce7578 at 2026-09-03 11:59:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 8 errors and 0 warnings.'
Found 8 errors and 0 warnings.
++ [[ 8 -gt 0 ]]
++ cat /sw/BUILD/a235577028463ab1fb854c410688da6c7ec06891/O2Physics-code-check/errors.txt
ALICE3/TableProducer/alice3MulticharmFinder.cxx:242:15: error: member 'picMinConstDCAxy' of type 'const float' is const qualified [cppcoreguidelines-avoid-const-or-ref-data-members,-warnings-as-errors]
ALICE3/TableProducer/alice3MulticharmFinder.cxx:243:15: error: member 'picMinPtDepDCAxy' of type 'const float' is const qualified [cppcoreguidelines-avoid-const-or-ref-data-members,-warnings-as-errors]
ALICE3/TableProducer/alice3MulticharmFinder.cxx:244:15: error: member 'picMinConstDCAz' of type 'const float' is const qualified [cppcoreguidelines-avoid-const-or-ref-data-members,-warnings-as-errors]
ALICE3/TableProducer/alice3MulticharmFinder.cxx:245:15: error: member 'picMinPtDepDCAz' of type 'const float' is const qualified [cppcoreguidelines-avoid-const-or-ref-data-members,-warnings-as-errors]
ALICE3/TableProducer/alice3MulticharmFinder.cxx:246:15: error: member 'piccMinConstDCAxy' of type 'const float' is const qualified [cppcoreguidelines-avoid-const-or-ref-data-members,-warnings-as-errors]
ALICE3/TableProducer/alice3MulticharmFinder.cxx:247:15: error: member 'piccMinPtDepDCAxy' of type 'const float' is const qualified [cppcoreguidelines-avoid-const-or-ref-data-members,-warnings-as-errors]
ALICE3/TableProducer/alice3MulticharmFinder.cxx:248:15: error: member 'piccMinConstDCAz' of type 'const float' is const qualified [cppcoreguidelines-avoid-const-or-ref-data-members,-warnings-as-errors]
ALICE3/TableProducer/alice3MulticharmFinder.cxx:249:15: error: member 'piccMinPtDepDCAz' of type 'const float' is const qualified [cppcoreguidelines-avoid-const-or-ref-data-members,-warnings-as-errors]
++ [[ 0 -gt 0 ]]
++ [[ 8 -gt 0 ]]
++ exit 1
--

Full log here.