dsa/dsa_pmeth.c: Add the checks for the EVP_MD_CTX_get_size()

Add the checks for the return value of EVP_MD_CTX_get_size() before explicitly cast them to size_t to avoid the integer overflow.

Fixes: 9d04f834 ("Add DSA digest length checks.")
Signed-off-by: Jiasheng Jiang <jiasheng@purdue.edu>

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Todd Short <todd.short@me.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23954)