fixed more overflow bugs in the multi-core bucketer
fixed more overflow bugs in the multi-core bucketer

[git-p4: depot-paths = "//sw/gpgpu/nvbio/main/": change = 18541072]

kimrutherford/nvbio,NVlabs/nvbio,kimrutherford/nvbio,kimrutherford/nvbio,kimrutherford/nvbio,NVlabs/nvbio,NVlabs/nvbio,NVlabs/nvbio