Protection for pt=0 ghost candidates in jet flavor clustering (71X)

[ferencek]

Backport of #9186

[cmsbuild]

A new Pull Request was created by @ferencek (Dinko Ferencek) for CMSSW_7_1_X.

Protection for pt=0 ghost candidates in jet flavor clustering (71X)

It involves the following packages:

PhysicsTools/JetMCAlgos

@cmsbuild, @vadler, @nclopezo, @monttj can you please review it and eventually sign? Thanks.
@ferencek, @acaudron, @pvmulder, @imarches this is something you requested to watch as well.
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[cmsbuild]

+1
Tested at: 3c483a3
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-9190/4900/summary.html

[davidlange6]

we don't care about this area in 71x, but merging anyway as this is a simple bug fix