[FileFormats.LP] fix reading variable with negative upper bound

[odow]

x-ref https://github.com/NVIDIA/cuopt/pull/1120/changes#r3127185613

I think this is a dumb rule, but indeed:

(base) odow@Mac /tmp % cat bug.lp 
maximize x
subject to
bounds
x <= -1.0
end
(base) odow@Mac /tmp % gurobi_cl bug.lp 
Set parameter WLSAccessID
Set parameter WLSSecret
Set parameter LicenseID to value 722777
Set parameter LogFile to value "gurobi.log"
Using license file /Users/odow/gurobi.lic
WLS license 722777 - registered to JuMP Development

Gurobi Optimizer version 12.0.3 build v12.0.3rc0 (mac64[arm] - Darwin 24.6.0 24G419)
Copyright (c) 2025, Gurobi Optimization, LLC

Read LP format model from file bug.lp
Reading time = 0.00 seconds
: 0 rows, 1 columns, 0 nonzeros

Using Gurobi shared library /Library/gurobi1203/macos_universal2/lib/libgurobi120.dylib

CPU model: Apple M4
Thread count: 10 physical cores, 10 logical processors, using up to 10 threads

WLS license 722777 - registered to JuMP Development
Optimize a model with 0 rows, 1 columns and 0 nonzeros
Model fingerprint: 0xd939e866
Coefficient statistics:
  Matrix range     [0e+00, 0e+00]
  Objective range  [1e+00, 1e+00]
  Bounds range     [1e+00, 1e+00]
  RHS range        [0e+00, 0e+00]
Presolve time: 0.00s

Solved in 0 iterations and 0.00 seconds (0.00 work units)
Infeasible model

Traced to #1810. I guess I just assumed what the correct behaviour was instead of looking into it in more detail.

[odow]

Test failure is #2995