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. 
It's a bug fix but:
iEtaSl could have been initialized as nBinsEta-1 (given EtaBins[0] = 0), loop to nBinsEta-2 above  and not bother at all here. Similar for brem (second line). Last bin of EtaBins[] and BremBins[] is then not needed.