ts/ts_rsp_sign.c: Add the check for the EVP_MD_CTX_get_size()

ts/ts_rsp_sign.c: Add the check for the EVP_MD_CTX_get_size()

Add the check for the return value of EVP_MD_CTX_get_size() to avoid invalid negative numbers.

Fixes: c7235be6e3 ("RFC 3161 compliant time stamp request creation, response generation and response verification.")
Signed-off-by: Jiasheng Jiang <jiasheng@purdue.edu>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23960)