crypto/pkcs12/p12_mutl.c: Add check and EVP_MD_free() for EVP_MD_fetch()

Add check and EVP_MD_free() for EVP_MD_fetch() to avoid NULL pointer
dereference and memory leak, like "md_fetch".

Fixes: fe79159b ("Implementation of the RFC 9579, PBMAC1 in PKCS#12")
Signed-off-by: Jiasheng Jiang <jiashengjiangcool@outlook.com>

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/25370)

(cherry picked from commit f60b3c5f)