[PWGCF] Fix bug in FV0 eta calculation

[abmodak]

1. Fix the initialisation of fv0det geometry pointer
2. Add addHistos function instead of using addClone

[github-actions]

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

[victor-gonzalez]

Thanks for considering my suggestions!

I have an additional one for security and error avoidance in case you want to also consider it

I would suggest not trusting on remembering the meaning of 0 or 3 or of the position in the template parameters
Two additional enums can be defined

enum KindOfMixing {
  kSE,
  kME
};

enum KindOfMultiplicity {
  kFT0AGLOBAL,
  kFT0CGLOBAL,
  kFV0GLOBAL,
  kMFTGLOBAL,
  kFV0MFT
};

and the functions can be templated with this types, for instance

  template <KindOfMultiplicity corrType, KindOfMixing evntType>
  void addHistos(...)

Now if always the named constants are used the compiler will advice if there is a misuse at any point

addHistos<kFT0GLOBAL, kSE>(...)

will compile correctly but

addHistos<kSE, kFT0GLOBAL>(...)

will give an error

The chosen names are, of course, representative

[victor-gonzalez]

Have a look at my additional comment in case you want to consider it for future iterations