Fix PFClusterProducer For ConfDB

[Martin-Grunewald]

ConfDB uses static templates with always all parameters. Hence a plugin should not behave differently if a
parameter is present in the py config or not. This fix replaces that logic by checking the value of the added
InputTag: if it is empty, the old behaviour (as was without this parameter present) is obtained.

[cmsbuild]

A new Pull Request was created by @Martin-Grunewald (Martin Grunewald) for CMSSW_7_0_X.

Fix PFClusterProducer For ConfDB

It involves the following packages:

RecoParticleFlow/PFClusterProducer

@nclopezo, @cmsbuild, @thspeer, @slava77 can you please review it and eventually sign? Thanks.
You can sign-off by replying to this message having '+1' in the first line of your reply.
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@ktf you are the release manager for this.

[cmsbuild]

+1
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-1754/1689/summary.html

[thspeer]

Working @thspeer

[thspeer]

+1
tested 12c35bd in CMSSW_7_0_X_2013-12-11-0200-1754
no difference on reco as expected.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next IBs unless changes or unless it breaks tests. @ktf can you please take care of it?