test/evp_extra_test.c: fix null pointer dereference
test/evp_extra_test.c: fix null pointer dereference

It's actually not a real issue but caused by the absence of the default case
which does not occur in reality but which makes coverity see a code path where
pkey remains unassigned.

Reported by Coverity Scan (CID 1423323)
[extended tests]

Reviewed-by: Nicola Tuveri <5a38b4ac03c90be61ead22c1d11b6e9f49425984@gmail.com>
Reviewed-by: Matt Caswell <1fa2ef4755a9226cb9a0a4840bd89b158ac71391@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7158)

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