[Rivet] PseudoJets constructor

[David Grellscheid]

Hi!

David Winn and I noticed a bug in FastJet: the empty constructor for 
PseudoJet leaves the member variables undefined instead of zeroing them.

This makes it impossible to write constructs like

PseudoJet sum;
for (....)
    sum += jet;

because the initial 'sum' has undefined values.


Instead of PseudoJet() {}, you need to explicitly set the values as
PseudoJet() : _px(), _py(), _pz(), _E() {}

This is a problem for any class that can be default-constructed.

See you,

   David