Avoid seg fault in HTXSRivetProducer

[Dr15Jones]

PR description:

If used in a job which processes no events, HTXSRivetProducer no longer seg faults.

PR validation:

Code compiles.

[Dr15Jones]

This should fix the crash seen in

https://cmssdt.cern.ch/SDT/cgi-bin/logreader/slc7_amd64_gcc900/CMSSW_11_3_X_2021-01-06-2300/pyRelValMatrixLogs/run/547.0_DYToll01234Jets_5f_LO_MLM_Madgraph_LHE_13TeV+DYToll01234Jets_5f_LO_MLM_Madgraph_LHE_13TeV+Hadronizer_TuneCP5_13TeV_MLM_5f_max4j_LHE_pythia8+NANOGENFromGen/step3_DYToll01234Jets_5f_LO_MLM_Madgraph_LHE_13TeV+DYToll01234Jets_5f_LO_MLM_Madgraph_LHE_13TeV+Hadronizer_TuneCP5_13TeV_MLM_5f_max4j_LHE_pythia8+NANOGENFromGen.log#/

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-32621/20676

• This PR adds an extra 12KB to repository

[Dr15Jones]

please test

[cmsbuild]

A new Pull Request was created by @Dr15Jones (Chris Jones) for master.

It involves the following packages:

GeneratorInterface/RivetInterface

@alberto-sanchez, @SiewYan, @agrohsje, @mkirsano, @GurpreetSinghChahal can you please review it and eventually sign? Thanks.
@alberto-sanchez, @mkirsano this is something you requested to watch as well.
@silviodonato, @dpiparo, @qliphy you are the release manager for this.

cms-bot commands are listed here

[cmsbuild]

+1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-e6996d/12035/summary.html
COMMIT: 132a719
CMSSW: CMSSW_11_3_X_2021-01-08-1100/slc7_amd64_gcc900

Comparison Summary

Summary:

• No significant changes to the logs found
• Reco comparison results: 7 differences found in the comparisons
• DQMHistoTests: Total files compared: 37
• DQMHistoTests: Total histograms compared: 2716967
• DQMHistoTests: Total failures: 12
• DQMHistoTests: Total nulls: 1
• DQMHistoTests: Total successes: 2716932
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.004 KiB( 36 files compared)
• DQMHistoSizes: changed ( 312.0 ): 0.004 KiB MessageLogger/Warnings
• Checked 156 log files, 37 edm output root files, 37 DQM output files

[SiewYan]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next master IBs (tests are also fine). This pull request will now be reviewed by the release team before it's merged. @silviodonato, @dpiparo, @qliphy (and backports should be raised in the release meeting by the corresponding L2)

[qliphy]

+1