A bug in a ring with matrix ordering

Let us create a ring with a matrix ordering:
{{{
> intmat m[3][3] = 3, 0, 1, 0, 1, 0, 0, 0, 1;
> ring R = 0, (x,y,z), M(m);
> x > 1;
1
> y > 1;
1
> z > 1;
1
}}}
Hence the monomial ordering of R is a well-ordering, and the value of internal attribute `OrdSgn` of R should be 1. But presently `OrdSgn` of R is set to -1. There seems to be a bug in the implementation of `rCheckOrdSgn` function in `libpolys/polys/monomials/ring.cc` file.

This bug was revealed while fixing a bug of Sage tracked in #28954.

fixed with git commit 3484489a559567285e5422a2a18fd88fb5a60600
Author: Hans Schoenemann <hannes@mathematik.uni-kl.de>
Date: Fri Jan 10 14:53:21 2020 +0100

fix: OrdSgn for matrix orderings with 0 in first row

I checked that the patch works well in Sage. Thank you!