Protection against empty globalDirs

[BetterWang]

(cherry picked from commit eecbc97)
Protection against empty vector.
Same as #15053

[cmsbuild]

A new Pull Request was created by @BetterWang (Quan Wang) for CMSSW_8_0_X.

It involves the following packages:

RecoPixelVertexing/PixelLowPtUtilities

@cmsbuild, @cvuosalo, @slava77, @davidlange6 can you please review it and eventually sign? Thanks.
@makortel, @GiacomoSguazzoni, @dgulhan, @rovere, @VinInn this is something you requested to watch as well.
@slava77, @Degano, @smuzaffar you are the release manager for this.

cms-bot commands are list here #13028

[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/13856/console

[cmsbuild]

+1
Tested at: 14c24ec
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-15101/13856/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-15101/13856/summary.html

[slava77]

+1

for #15101 14c24ec

• the same fix as in 81X Protection against empty globalDirs #15100 and 75X Protection against empty globalDirs #15053. This should affect only events that would otherwise lead to a crash.
• jenkins tests pass and comparisons show no differences.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_8_0_X IBs (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @slava77, @davidlange6, @Degano, @smuzaffar

[davidlange6]

+1