Dereferencing a pointer that might be null key_token when calling strstr.
Check if the pointer is null before.
Coverity issue: 141071
Fixes: f8be1786b1b8 ("app/crypto-perf: introduce performance test application")
Signed-off-by: Slawomir Mrozowicz <slawomirx.mrozowicz@intel.com>
Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>