poincare in presence of degree zero variables

[mahrud]

Perhaps it should give an error instead:

i1 : R = kk[x,y, Degrees => {0,1}]

o1 = R

o1 : PolynomialRing

i2 : poincare ideal (x,y)

o2 = 0

o2 : ZZ[T]

i8 : poincare ideal (x+y^2)

          2
o8 = 1 - T

o8 : ZZ[T]

c.f. https://github.com/Macaulay2/M2/issues/909