ERR: fix err_data_size inconsistencies

ERR: fix err_data_size inconsistencies

In ERR_add_error_vdata(), the size of err_data had 1 added to it in
some spots, which could lead to buffer overflow.

In ERR_vset_error(), ERR_MAX_DATA_SIZE was used instead of buf_size in
the BIO_vsnprintf() call, which would lead to a buffer overflow if
such a large buffer couldn't be allocated.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/9491)