Fix ORC reader issue with bystream reader (#7988)

Resolves issue with ORC reader.

There were two issues,

There was a missing check to keep number of streams that needs to be accessed.
The position which was being used to calculate buffer length was wrong, and assigned non-zero value for a stream whose length is zero.

Authors:
  - Ram (Ramakrishna Prabhu) (https://github.com/rgsl888prabhu)

Approvers:
  - Ayush Dattagupta (https://github.com/ayushdg)
  - Paul Taylor (https://github.com/trxcllnt)
  - Devavret Makkar (https://github.com/devavret)

URL: #7988

cpp/src/io/orc/stripe_data.cu

@@ -149,9 +149,9 @@ static __device__ void bytestream_init(volatile orc_bytestream_s *bs,
                                        const uint8_t *base,
                                        uint32_t len)
 {
-  uint32_t pos   = static_cast<uint32_t>(7 & reinterpret_cast<size_t>(base));
+  uint32_t pos   = (len > 0) ? static_cast<uint32_t>(7 & reinterpret_cast<size_t>(base)) : 0;
   bs->base       = base - pos;
-  bs->pos        = (len > 0) ? pos : 0;
+  bs->pos        = pos;
   bs->len        = (len + pos + 7) & ~7;
   bs->fill_pos   = 0;
   bs->fill_count = min(bs->len, bytestream_buffer_size) >> 3;

cpp/src/io/orc/stripe_init.cu

@@ -40,7 +40,7 @@ extern "C" __global__ void __launch_bounds__(128, 8) gpuParseCompressedStripeDat
   int strm_id                  = blockIdx.x * 4 + (threadIdx.x / 32);
   int lane_id                  = threadIdx.x % 32;
 
-  if (lane_id == 0) { s->info = strm_info[strm_id]; }
+  if (strm_id < num_streams && lane_id == 0) { s->info = strm_info[strm_id]; }
 
   __syncthreads();
   if (strm_id < num_streams) {