Avoid null reference in getTrackFromChargedHadron

[Dr15Jones]

PR description:

Calling operator* on a edm:Ref can cause it to return a reference to a nullptr. This is not allowed in C++ which allows the compiler to remove checks. This lead to crashes when clang optimized the
code. Getting a pointer instead avoids the problem.

PR validation:

Ran workflow 4.23 which was crashing under CMSSW_10_6_CLANG_X_2019-04-07-0000 but now
runs fine with this change.

[cmsbuild]

The code-checks are being triggered in jenkins.

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-26381/9130

• This PR adds an extra 12KB to repository

[cmsbuild]

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

It involves the following packages:

RecoTauTag/RecoTau

@cmsbuild, @perrotta, @slava77 can you please review it and eventually sign? Thanks.
@davidlange6, @slava77, @fabiocos you are the release manager for this.

cms-bot commands are listed here

[perrotta]

please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/34041/console Started: 2019/04/08 07:08

[cmsbuild]

+1
Tested at: ac6051b
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-26381/34041/summary.html

[cmsbuild]

Comparison job queued.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-26381/34041/summary.html

Comparison Summary:

• No significant changes to the logs found
• Reco comparison results: 4 differences found in the comparisons
• DQMHistoTests: Total files compared: 32
• DQMHistoTests: Total histograms compared: 3140495
• DQMHistoTests: Total failures: 1
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 3140297
• DQMHistoTests: Total skipped: 197
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 31 files compared)
• Checked 133 log files, 14 edm output root files, 32 DQM output files

[slava77]

+1

for #26381 ac6051b

• code changes are in line with the PR description
• jenkins tests pass and comparisons with the baseline show no differences

[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. @davidlange6, @slava77, @smuzaffar, @fabiocos (and backports should be raised in the release meeting by the corresponding L2)

[fabiocos]

+1