fixed bug in OMP reduce() when [first,last) defines an empty range
fixed bug in OMP reduce() when [first,last) defines an empty range

--HG--
extra : convert_revision : svn%3A83215879-3e5a-4751-8c9d-778f44bb06a5/trunk%40714

egaburov/thrust,zhenglaizhang/thrust,xiongzhanblake/thrust,Ricardo666666/thrust,thrust/thrust,dachziegel/thrust,xiongzhanblake/thrust_src,zeryx/thrust,egaburov/thrust,xiongzhanblake/thrust_src,sdalton1/thrust,arnabgho/thrust,egaburov/thrust,sarvex/thrust,mohamed-ali/thrust,andrewcorrigan/thrust-multi-permutation-iterator,raygit/thrust,zeryx/thrust,dachziegel/thrust,zeryx/thrust,jaredhoberock/thrust,zhenglaizhang/thrust,arnabgho/thrust,sarvex/thrust,marksantos/thrust,dachziegel/thrust,marksantos/thrust,thrust/thrust,jaredhoberock/thrust,zhenglaizhang/thrust,arnabgho/thrust,jaredhoberock/thrust,sdalton1/thrust,jaredhoberock/thrust,xiongzhanblake/thrust_src,xiongzhanblake/thrust,thvasilo/thrust,sdalton1/thrust,andrewcorrigan/thrust-multi-permutation-iterator,thrust/thrust,Ricardo666666/thrust,marksantos/thrust,raygit/thrust,mohamed-ali/thrust,xiongzhanblake/thrust,raygit/thrust,thvasilo/thrust,andrewcorrigan/thrust-multi-permutation-iterator,thvasilo/thrust,GrimDerp/thrust,thrust/thrust,GrimDerp/thrust,thrust/thrust,GrimDerp/thrust,mohamed-ali/thrust,sarvex/thrust,jaredhoberock/thrust,Ricardo666666/thrust