Fix crash in HcalDigisClient for SLHC configurations

[mark-grimes]

Moved the initialisation of doSLHC_ to before the histograms are booked.

An extra set of histograms are booked in the "booking(...)" method if doSLHC_ is true. If doSLHC_ is not initialised before these calls then the choice whether to book them or not is made on uninitialised memory.

[cmsbuild]

A new Pull Request was created by @mark-grimes (Mark Grimes) for CMSSW_6_2_X_SLHC.

Fix crash in HcalDigisClient for SLHC configurations

It involves the following packages:

Validation/HcalDigis

@ojeda, @danduggan, @rovere, @cmsbuild, @nclopezo, @deguio, @Degano can you please review it and eventually sign? Thanks.
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@andersonjacob, @mark-grimes you are the release manager for this.
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[mark-grimes]

merge

Is there a protocol for accepting my own pull requests? Anyway, this is needed because otherwise all the other other pull requests I'm testing will randomly pass or fail some of the tests. Tested with #2405 on top which was previously causing crashes. All these tests now pass:
3400 with combinedCustoms.cust_2019WithGem
Extended pixel GEN-SIM test
3300, 3400, 4100, 4400, 40001, 50002, 60002, 4502, 4500, 5001 and 15001