Found two crashes caused by two defects in preprocess_kernels.cu

[Arnold Chen]

Hello, we saw sometime crashes happened in our application with CUDA-PointPillars integrated, after investigated and found the causes are in preprocess_kernels.cu.

1. in generateVoxels_random_kernel():

   int voxel_idx = floorf((point.x - min_x_range)/pillar_x_size);
   int voxel_idy = floorf((point.y - min_y_range)/pillar_y_size);
   our grid_y_size is 320, when (point.y - min_y_range)/pillar_y_size == 319.999998, voxel_idy = floorf(319.999998), the value of voxel_idy is 320 not 319 ! voxel_idy == grid_y_size, this caused invalid out-of-bounding access to mask and voxels, and the memory was then corrupted, so, a crash happened accordingly.

2. in generateBaseFeatures_kernel():
   current_pillarId = atomicAdd(pillar_num, 1);
   Hereafter no checking is done for current_pillarId, if there are points scattering in a very large range and current_pillarId is greater than MAX_VOXELS(40000), memory will be corrupted by "((float4*)voxel_features)[outIndex] = ((float4*)voxels)[inIndex];" because of invalid out-of-bounding access to voxel_features.

Did a sample fix here: arnoldfychen@2c9c4a1
then no crash was seen.