BUG: initialize m_SmallBlock ivar in ctor; fixes garbage read

fixes clang ubsan error in itkGPUReductionTest test:
Modules/Core/GPUCommon/include/itkGPUReduction.hxx:225:20: runtime error: load of value 170, which is not a valid value for type 'bool'

Initialized a couple of other ivars while I was there.

Change-Id: I95b193876386cc7ca42f0807d2a8e9b75e76a6e1
BUG: changed some variables involved in shifting to unsigned

fixes clang ubsan error in itkGE4 test:
Modules/IO/GE/src/itkGE4ImageIO.cxx:375:29: runtime error: left shift of negative value -2113929216

Also:
- removed unused #defines
- removed useless casts
- put declarations with initializations.

Change-Id: Iab8d861afcc912934ac0bd7df486950fc59d4174
Merge topic 'ubsan-fixes'

830538d BUG: changed some variables involved in shifting to unsigned
bd2c342 BUG: initialize m_SmallBlock ivar in ctor; fixes garbage read