reco comparisons driver: check that both input root files are available before running validate.C

[slava77]

while testing cms-sw/cmssw#32325 (comment)
Reco comparison had 1 failed jobs showed up somewhat unexpectedly.
It was triggered by a request to include a workflow in the test which does not have a reference. These unpaired inputs should not be used to run validate.C (fwlite-based reco comparisons).

this PR should resolve the issue

[cmsbuild]

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

@cmsbuild, @smuzaffar, @mrodozov can you please review it and eventually sign? Thanks.
cms-bot commands are listed here

[slava77]

@cmsbuild please test workflow 140.5611 with cms-sw/cmssw#32325

[cmsbuild]

The tests are being triggered in jenkins.
Tested with other pull request(s) cms-sw/cmssw#32325
Test Parameters:

• MATRIX_EXTRAS = 140.5611
• CMSSW_11_3_X_2020-11-30-1100/slc7_amd64_gcc900: https://cmssdt.cern.ch/jenkins/job/ib-run-pr-tests/11191/console Started: 2020/12/01 04:17

[cmsbuild]

+1
Tested at: 3f8af83
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-d690f3/11191/summary.html
CMSSW: CMSSW_11_3_X_2020-11-30-1100
SCRAM_ARCH: slc7_amd64_gcc900

[cmsbuild]

Comparison job queued.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-d690f3/11191/summary.html

Comparison Summary:

• No significant changes to the logs found
• Reco comparison results: 9 differences found in the comparisons
• DQMHistoTests: Total files compared: 35
• DQMHistoTests: Total histograms compared: 2529593
• DQMHistoTests: Total failures: 13
• DQMHistoTests: Total nulls: 1
• DQMHistoTests: Total successes: 2529557
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.004 KiB( 34 files compared)
• DQMHistoSizes: changed ( 312.0 ): 0.004 KiB MessageLogger/Warnings
• Checked 148 log files, 34 edm output root files, 35 DQM output files

[smuzaffar]

+externals

[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. @silviodonato, @dpiparo, @qliphy (and backports should be raised in the release meeting by the corresponding L2)