Solve fails on problem with only 1 variable

The following code runs correctly for `count = 2`, but fails with `count = 1`.

```
#!/usr/bin/env python

from cylp.cy import CyClpSimplex
from cylp.py.modeling.CyLPModel import CyLPArray

count = 2

s = CyClpSimplex()
x = s.addVariable('x', count)

s += 0.0 <= x <= 10.0

s.objective = CyLPArray([20]*count) * x
s.optimizationDirection = 'max'

status = s.primal()
result = s.primalVariableSolution['x']

print(status)
print(result)
```

The error raised:

```
meh.py:9: FutureWarning: comparison to `None` will result in an elementwise object comparison in the future.
x = s.addVariable('x', count)
meh.py:12: FutureWarning: comparison to `None` will result in an elementwise object comparison in the future.
s += 0.0 <= x <= 10.0
Traceback (most recent call last):
File "meh.py", line 14, in
s.objective = CyLPArray([20]*count) * x
File "CyClpSimplex.pyx", line 141, in cylp.cy.CyClpSimplex.CyClpSimplex.objective.__set__ (cylp/cy/CyClpSimplex.cpp:4559)
File "CyClpSimplex.pyx", line 1192, in cylp.cy.CyClpSimplex.CyClpSimplex.setObjectiveArray (cylp/cy/CyClpSimplex.cpp:17461)
ValueError: Buffer has wrong number of dimensions (expected 1, got 0)
```

This can be worked around by adding another variable, which can be completely unconstrained and not included in the objective function definition. However, this shouldn't be required.