`FSTrackMapLookup` called two times in FairStack

[ChristianTackeGSI]

@dennisklein already noticed this in #1584, filing an issue now.

For FairStack, FSTrackMapLookup is called on its own result.

Current dev branch:

FairRoot/fairroot/base/sim/FairGenericStack.cxx

Line 133 in 6decd1e

Int_t const trackID = FSTrackMapLookup(GetCurrentTrackID());

FairRoot/fairroot/base/sim/FairGenericStack.h

Line 49 in 6decd1e

Int_t GetCurrentTrackID() const { return GetCurrentTrackNumber(); }

FairRoot/examples/common/mcstack/FairStack.cxx

Lines 240 to 243 in 6decd1e

	Int_t FairStack::GetCurrentTrackNumber() const
	{
	return FSTrackMapLookup(fCurrentTrack);
	}

As I don't understand this FastSim things, I can't propose a solution. So I can only report this.