Fix infloop in neutbgr

[civanch]

This PR fixing infinite loop in neutron background simulation.

[civanch]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_6_2_X_SLHC IBs unless changes or unless it breaks tests. @fratnikov, @mark-grimes can you please take care of it?

[fratnikov]

merge
passed tests with single pions
12261 failed in step 4 with
----- Begin Fatal Exception 19-Jun-2014 04:53:07 CEST-----------------------
An exception of category 'Conditions not found' occurred while
[0] Processing run: 1
[1] Running path 'dqmHarvesting'
[2] Calling beginRun for module HcalMonitorClient/'hcalClient'
Exception Message:
Unavailable HcalCalibrations for cell (HE -29,1,1)
----- End Fatal Exception -------------------------------------------------

which is irrelevant to this PR