common/cpt: fix component for empty IOV buffer

common/cpt: fix component for empty IOV buffer

fill_sg_comp_from_iov() prepares gather components for i/p IOV
buffers and extra buf. This API is failing to create a gather component
for extra_buf when IOV buf len is zero. Though there is enough space
to accommodate extra_buf, because of pre-decrementing of extra_buf
length from aggregate size, this issue is seen.

Fixes: b74652f3a91f ("common/cpt: add microcode interface for encryption")
Cc: stable@dpdk.org
Signed-off-by: Archana Muniganti <marchana@marvell.com>
Signed-off-by: Anoob Joseph <anoobj@marvell.com>