Fix out of bound array in photon uncertainty calculation

[cmsbuild]

Old photon uncertainty calculation was trying to access array index -1.
Added protection against that.

This modification concerns only an outdated energy correction that should not be used anymore. Thus, this should not affect any current usage of RecoEgamma.
Automatically ported from CMSSW_7_5_X #9381 (original by @rafaellopesdesa).

[cmsbuild]

A new Pull Request was created by @cmsbuild for CMSSW_7_6_X.

Fix out of bound array in photon uncertainty calculation

It involves the following packages:

RecoEgamma/EgammaPhotonAlgos

@cmsbuild, @cvuosalo, @slava77 can you please review it and eventually sign? Thanks.
@Sam-Harper, @lgray this is something you requested to watch as well.
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@Degano you are the release manager for this.
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[cmsbuild]

Pull request #9821 was updated. @cmsbuild, @cvuosalo, @slava77 can you please check and sign again.

[cvuosalo]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

Pull request #9821 was updated. @cmsbuild, @cvuosalo, @slava77 can you please check and sign again.

[cmsbuild]

+1
Tested at: 1ccf013
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-9821/186493/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-9821/186493/summary.html

[cvuosalo]

+1

For #9821 1ccf013

Protect against incorrect array reference used to calculate photon uncertainty. #9831, the matching PR for 75X, has already been approved by Reco.

The code changes are satisfactory, and Jenkins tests against baseline CMSSW_7_6_X_2015-06-23-1100 show no significant differences.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_6_X IBs (tests are also fine). This pull request will be automatically merged.