Avoid crash of GenParticles2HepMCConverter

[jhgoh]

Same for #5532

The GenParticles2HepMCConverter can crash if a particle's pdgId is not present in the HepPDT while setting the generated_mass.
The problem was spotted by Bhawan.
Query to get particle info with pdgId=102112 returns null pointer, causes segmentation fault.

As a solution, particle's generated_mass in HepMC is assigned to be same as the GenParticle's mass itself if it fails to get particle from PDT.
This is safe for the Rivet analysis since this information shouldn't be used in the particle level analysis.

[cmsbuild]

A new Pull Request was created by @jhgoh (Junghwan John Goh) for CMSSW_7_3_X.

Avoid crash of GenParticles2HepMCConverter

It involves the following packages:

GeneratorInterface/RivetInterface

@vciulli, @cmsbuild, @nclopezo, @bendavid, @thuer can you please review it and eventually sign? Thanks.
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@nclopezo, @ktf you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[bendavid]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_3_X IBs unless changes or unless it breaks tests. @nclopezo, @ktf can you please take care of it?

[cmsbuild]

+1
Tested at: 41daaa3
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-5533/1/summary.html