apps: lib: Prevent potential NULL dereference in init_client()

apps: lib: Prevent potential NULL dereference in init_client()

apps: lib: Simplify ba_ret handling in init_client()

Simplify logic around ba_ret assignment:
- Fail early if ba_ret == NULL
- Assign directly otherwise, without checking *ba_ret

This avoids extra nesting and matches OpenSSL's conventions.

CLA: trivial
Signed-off-by: Anton Moryakov <ant.v.moryakov@gmail.com>
Co-authored-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26783)