apps/rehash.c: Add the check for the EVP_MD_get_size()

apps/rehash.c: Add the check for the EVP_MD_get_size()

Add the check for the return value of EVP_MD_get_size() to avoid invalid negative
numbers and then explicitly cast from int to size_t.

Add the check to prevent that EVP_MD_get_size() returns a value greater
than EVP_MAX_MD_SIZE.

Signed-off-by: Jiasheng Jiang <jiashengjiangcool@outlook.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/24802)