fuzz/provider.c: Add check for OPENSSL_malloc() to avoid potential NULL pointer deref...

fuzz/provider.c: Add check for OPENSSL_malloc() to avoid potential NULL pointer dereference

Add check for the return value of OPENSSL_malloc() to avoid potential NULL pointer dereference.

Fixes: f3b988d ("Add provider fuzzer")
Signed-off-by: Jiasheng Jiang <jiashengjiangcool@gmail.com>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Frederik Wedel-Heinen <fwh.openssl@gmail.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/27868)