fix array index out of bounds in mip fraction

This fixes a small bug with an out-of-bounds array index when determining the MIP fraction for FastSim hadronic showers. This caused the code to grab values out of neighboring memory. The bug only affects hadrons with energy > 3 TeV, so the effect on simulation results should be small.

Example of buggy behavior (from a few 5 TeV pion events):
Begin processing the 1st record. Run 1, Event 1, LumiSection 1 at 14-Jul-2014 21:06:57.152 CEST
CalorimetryManager onHcal 6.92421e-310
CalorimetryManager onHcal 6.92421e-310
Begin processing the 2nd record. Run 1, Event 2, LumiSection 1 at 14-Jul-2014 21:07:02.608 CEST
CalorimetryManager onHcal 0.99857
CalorimetryManager onHcal 0.99618

Example of fixed behavior:
Begin processing the 1st record. Run 1, Event 1, LumiSection 1 at 14-Jul-2014 21:31:38.048 CEST
CalorimetryManager onHcal 0.09604
CalorimetryManager onHcal 0.09294
Begin processing the 2nd record. Run 1, Event 2, LumiSection 1 at 14-Jul-2014 21:31:42.721 CEST
CalorimetryManager onHcal 0.01353
CalorimetryManager onHcal 0.03486

I don't think so...

y1, y2 are declared
x1 is declared and initialized
x2 is declared and initialized
y1 is initialized
y2 is initialized

Nothing is repeated... For some reason, in the old version the declaration of y1, y2 was indented multiple times, so I just removed the indents to make it look nicer.