fix array overflow issues found by David A.

Issues reported at
https://hypernews.cern.ch/HyperNews/CMS/get/swReleases/4108/1/1/1/1/1/1/1/1.html
and follow ups are mostly fixed here. 
@lgray @Sam-Harper
Shouldn't this be ```if (eta>=EtaBins[nBinsEta]) iEtaSl = nBinsEta-1;``` ?
(note the possible equality since it's not covered in the logic above)

and, similalrly, below ```if (brem>=BremBins[nBinsBrem]) iBremSl = nBinsBrem-1;```