bug in computing syzygy module for tower rings involving the Weyl algebra in the presence of Schreyer orders

Greg Smith and I ran across the following bug.
```
R = ZZ/101[s,t, Degrees => {0,0}]/(s^2-t^2-1)
S = R[x,y,Dx,Dy, WeylAlgebra => {{x,Dx}, {y,Dy}}, Degrees => {1, 1, -1, -1}, Join => false]
I = ideal(x*Dx + s*t, y*Dx)
m = gens I
syz m -- ok
m1 = schreyerOrder m
syz m1 -- BUG!!
```

Either this should not be allowed or the code the code should be fixed (preferable), but a divide by zero error is not optimal...!

The atttempt to divide by zero has a misspelling as well.

Start by reproducing the provided Macaulay2 example, focusing on the syz call after schreyerOrder m. Trace the divide-by-zero failure and its misspelled message; done means the case no longer fails with that error, either by fixing the computation or explicitly preventing the unsupported operation.

Written by the indexing model from the issue text.