rsa/rsa_ameth.c: Add the check for the EVP_MD_get_size()

rsa/rsa_ameth.c: Add the check for the EVP_MD_get_size()

Add the check for the EVP_MD_get_size() to avoid invalid negative numbers.

Fixes: 17c63d1cca ("RSA PSS ASN1 signing method")
Signed-off-by: Jiasheng Jiang <jiasheng@purdue.edu>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23973)