test/compress: fix some checks
test/compress: fix some checks

CID 340857: Null pointer dereferences (NULL_RETURNS)
CID 340856: (CONSTANT_EXPRESSION_RESULT)

Coverity issue: 340856, 340857
Fixes: 3be12ea52ad8 ("test/compress: improve debug trace setup")
Cc: stable@dpdk.org

Signed-off-by: Adam Dybkowski <b636839fd6da8c90d3d28fcb76555ed5d2c5a673@intel.com>
Acked-by: Fiona Trahe <7ba562cc372916cd557d0be347608f8b4da4f746@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk