Bug fix for unitialized pointers

Fix a bug related to unitialized pointers. With
standard configurations this bug will cause no problems.
But if someone changed the configured random engine
type to not be TRandom3 for FastSimulation it could
cause a seg fault. Bug was introduced in 7_0_X in
November.
Merge pull request #2461 from wddgit/bugFixUnitialized

FastSim fix -- Bug fix for uninitialized pointers
Merge remote branch 'origin/CMSSW_7_0_X' into CMSSW_7_0_X