avoid a crash in BTVHLTOfflineSource

[slava77]

trivial fix to avoid the crash in the recent IBs and in 800pre3.
https://cmssdt.cern.ch/SDT/cgi-bin/buildlogs/slc6_amd64_gcc493/CMSSW_8_0_X_2015-12-11-1100/pyRelValMatrixLogs/run/134.805_RunMET2015C+RunMET2015C+HLTDR2_25ns+RECODR2_25nsreHLT+HARVESTDR2_25nsreHLT/step3_RunMET2015C+RunMET2015C+HLTDR2_25ns+RECODR2_25nsreHLT+HARVESTDR2_25nsreHLT.log

Since the validation code didn't change, there may actually be a problem with the inputs.
That can be resolved in a follow up or a replacement PR

[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/10316/console

[cmsbuild]

A new Pull Request was created by @slava77 (Slava Krutelyov) for CMSSW_8_0_X.

It involves the following packages:

DQMOffline/Trigger

@cmsbuild, @vanbesien, @deguio, @davidlange6 can you please review it and eventually sign? Thanks.
@rociovilar, @trocino, @jhgoh, @battibass this is something you requested to watch as well.
@slava77, @Degano, @smuzaffar you are the release manager for this.

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[cmsbuild]

+1
Tested at: 65e74bf
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-12799/10316/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-12799/10316/summary.html

[slava77]

@deguio please check at your earliest
the crash shows up in several workflows that I use for local higher stat tests.
It would be better not to have it.

[deguio]

thanks,
F.