Issue 68 is not properly fixed

[wegank]

In #68, the input was

msolve/input_files/bug-68.ms

Lines 1 to 6 in 6c9d63e

	x,y,z
	257
	0,
	x*x+y*y+z*z,
	x+y+z,
	x+y*z

Here, x*x is not parsable by msolve, so the test already does not make sense. However, even if one write in input.ms

x,y,z
257
0,
x^2+y^2+z^2,
x+y+z,
x+y*z

The output of msolve -f input.ms -g 2 is wrong:

#Reduced Groebner basis data
#---
#field characteristic: 257
#variable order:       x, y, z
#monomial order:       graded reverse lexicographical
#length of basis:      2 elements sorted by increasing leading monomials
#---
[1*x^1+1*y^1+1*z^1,
1*y^2+1*y^1*z^1+1*z^2]:

In fact, removing 0 gives the correct output:

#Reduced Groebner basis data
#---
#field characteristic: 257
#variable order:       x, y, z
#monomial order:       graded reverse lexicographical
#length of basis:      4 elements sorted by increasing leading monomials
#---
[1*x^1+1*y^1+1*z^1,
1*y^1*z^1+256*y^1+256*z^1,
1*y^2+1*z^2+1*y^1+1*z^1,
1*z^3+1*y^1+1*z^1]:

What's worse, if one adds more zeros:

x,y,z
257
0,
0,
0,
x^2+y^2+z^2,
x+y+z,
x+y*z

Then msolve -f input.ms -g 2 hangs.