coverity #1486532: fix potential NULL dereference in test_mk_file_path()
coverity #1486532: fix potential NULL dereference in test_mk_file_path()

Reviewed-by: Ben Kaduk <b34e9dc3dd24827b45bb22e8b76cde1bcb413b0e@mit.edu>
Reviewed-by: Paul Dale <ddec78389666b4f7c9b4d110380c848489a3e4aa@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15942)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl