[openssl/openssl] 6ca1d3: fix missing null check in kdf_test_ctrl

[Neil Horman]

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: 6ca1d3ee81b61bc973e4e1079ec68ac73331c159
      https://github.com/openssl/openssl/commit/6ca1d3ee81b61bc973e4e1079ec68ac73331c159
  Author: Neil Horman <nhorman at openssl.org>
  Date:   2024-01-30 (Tue, 30 Jan 2024)

  Changed paths:
    M test/evp_test.c

  Log Message:
  -----------
  fix missing null check in kdf_test_ctrl

Coverity issue 1453632 noted a missing null check in kdf_test_ctrl
recently.  If a malformed value is passed in from the test file that
does not contain a ':' character, the p variable will be NULL, leading
to a NULL derefence prepare_from_text

Reviewed-by: Tomas Mraz <tomas at openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove at arm.com>
(Merged from https://github.com/openssl/openssl/pull/23398)