runs without a solution are not catched when using glpk

[phil-fzj]

Purpose of the improvement

When glpk fails to find a solution, the code just continues and only fails later with very cryptic error messages

TypeError: unsupported operand type(s) for *: 'float' and 'NoneType'

See this example:

Warning: basis matrix is ill-conditioned (cond = 1.14e+14)
Error: basis matrix is singular to working precision (cond = 4.54e+15)
glp_simplex: unable to recover undefined or non-optimal solution
If you need actual output for non-optimal solution, use --nopresol
Time used:   141.6 secs
Memory used: 73.7 Mb (77238063 bytes)
Writing basic solution to '/tmp/tmpuy8qxdh4.glpk.raw'...
92882 lines were written

Status: ok
Termination condition: other
Statistics: 
  Branch and bound: 
    Number of bounded subproblems: 0
    Number of created subproblems: 0
Error rc: 0
Time: 142.14720749855042


Name: unknown
Lower bound: -.inf
Upper bound: .inf
Number of objectives: 1
Number of constraints: 62110
Number of variables: 30763
Number of nonzeros: 182899
Sense: minimize

Solve time: 143.76304483413696 sec.
/fast/home/p-dunkel/testing/fine_gh/fine/energySystemModel.py:2162: UserWarning: Output is generated for a non-optimal solution.
  warnings.warn("Output is generated for a non-optimal solution.")

Processing optimization output...
Traceback (most recent call last):
  File "/fast/home/p-dunkel/testing/fine_gh/aaa.py", line 482, in <module>
    esM.optimize(timeSeriesAggregation=True, solver="glpk")
  File "/fast/home/p-dunkel/testing/fine_gh/fine/energySystemModel.py", line 2175, in optimize
    mdl.setOptimalValues(self, self.pyM)
  File "/fast/home/p-dunkel/testing/fine_gh/fine/sourceSink.py", line 965, in setOptimalValues
    optSummaryBasic = super().setOptimalValues(
                      ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/fast/home/p-dunkel/testing/fine_gh/fine/component.py", line 3860, in setOptimalValues
    resultsNPV_cx = self.getEconomicsDesign(
                    ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/fast/home/p-dunkel/testing/fine_gh/fine/component.py", line 3196, in getEconomicsDesign
    annuity = self.getLocEconomicsDesign(
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/fast/home/p-dunkel/testing/fine_gh/fine/component.py", line 3425, in getLocEconomicsDesign
    return factor * _var.value
           ~~~~~~~^~~~~~~~~~~~
TypeError: unsupported operand type(s) for *: 'float' and 'NoneType'

Proposal

Raise an error if no solution is available.
The user warning

UserWarning: Output is generated for a non-optimal solution.

is not sufficient, if there is no solution available at all!