[Common] Add protection for DFs with zero reco collisions in TPC PID module

[fgrosa]

This PR adds a protection for very rare cases of AO2Ds of MC productions, that do not contain any reconstructed collision. In these cases, the tracks have all collisionId = 0 and the current code crashes as it tries to access the 0-th entry of the vectors, which is not allocated.
Tagging @zhangbiao-phy for info

[github-actions]

O2 linter results: ❌ 22 errors, ⚠️ 34 warnings, 🔕 0 disabled

[alibuild]

Error while checking build/O2Physics/code-check for 0a3b274 at 2026-07-06 16:06:

++ set -euo pipefail
++ [[ -d /sw/slc9_x86-64/Clang/v20.1.7-20 ]]
+++ realpath /sw/BUILD/a64adf8c43b8d19ed3833c1a87ef6079239fffba/O2Physics-code-check/../../O2Physics-latest/O2Physics
++ O2PHYSICS_BUILDDIR=/sw/BUILD/c53f596a677b916f161f0238deb59391d1fed68c/O2Physics
++ cp /sw/BUILD/c53f596a677b916f161f0238deb59391d1fed68c/O2Physics/compile_commands.json .
+++ python3 -c 'import json, os; print(os.path.commonpath([x["file"] for x in json.loads(open("compile_commands.json").read()) if "sw/BUILD" not in x["file"] and "G__" not in x["file"] and x["file"].endswith(".cxx")]))'
++ O2PHYSICS_SRC=/sw/SOURCES/O2Physics/slc9_x86-64-slc9_x86-64/0
++ pushd /sw/SOURCES/O2Physics/slc9_x86-64-slc9_x86-64/0
/sw/SPECS/slc9_x86-64/O2Physics-code-check/1.0-local62/O2Physics-code-check.sh: line 16: pushd: /sw/SOURCES/O2Physics/slc9_x86-64-slc9_x86-64/0: No such file or directory

Full log here.