X509_VERIFY_PARAM_set1_name(): if invoked with NULL as the second
parameter, correctly set param->name to NULL after having freed it.
ok bcook@
X509_NAME_get_text_by_OBJ(): make sure we do not pass a negative size to
memcpy().
ok bcook@
check_cert(): be sure to reset ctx->current_crl to NULL before freeing it.

X509_STORE_CTX_init(): do not free the X509_STORE_CTX * parameter upon
failure, for we did not allocate it and it might not come from the heap,
such as in check_crl_path() in this very same file where X509_STORE_CTX_init()
gets invoked with a stack address.

ok bcook@
Previous fix (1.12) would cause a NULL pointer dereference in the error path
if a NULL stack was passed as argument. Fix this by returning NULL early in
that case.