fix (rare) crash in DYT muon reco

[slava77]

Fixes the crash reported in
https://hypernews.cern.ch/HyperNews/CMS/get/relval/3239.html

no changes expected in regular tests and none are observed (the condition for the crash is fairly rare)

@jhgoh please check the changes with the main developers.
My fix is just technical to avoid the crash, but it would be good to check in more details why
this condition happens.
The issue can be reproduced from http://cms-project-relval.web.cern.ch/cms-project-relval/failures/CMSSW_7_3_0_pre2/12Nov2014_1/JpsiMuMu_Pt-15_Job1.tar.gz
(dump the PSet.py there to see the expanded config details)

[slava77]

+1

for #6428 5dfaa9e

tested in CMSSW_7_3_0_pre2 (test area crash-dyt).
No changes are observed in the short matrix tests.
The crash in the pre2 relval job is not happening anymore.

[cmsbuild]

A new Pull Request was created by @slava77 (Slava Krutelyov) for CMSSW_7_3_X.

fix (rare) crash in DYT muon reco

It involves the following packages:

RecoMuon/GlobalTrackingTools

@cmsbuild, @nclopezo, @StoyanStoynev, @slava77 can you please review it and eventually sign? Thanks.
@battibass, @abbiendi, @bellan, @trocino, @bachtis, @rociovilar this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
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@nclopezo you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_3_X IBs unless changes or unless it breaks tests.

[cmsbuild]

+1
Tested at: 5dfaa9e
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6428/911/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_3_X IBs unless changes (tests are also fine). This pull request will be automatically merged.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6428/911/summary.html

[Dr15Jones]

@slava77 Thanks for the fix. I saw the exact same crash in the threaded build today and was worried it was a threading issue. Glad to see it is not :).

[cmsbuild]

+1
Tested at: 5dfaa9e
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6428/1135/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6428/1135/summary.html