Validation log never gets an update after the first API run

[maxkratz]

Currently, the validation log in the GipsEngine will be set before the first run of the ILP solver. If the model changes afterward (e.g., the constraint that invalidated the problem vanishes), the validation log does not get an update and, therefore, breaks the following solving runs.

Example (taken from https://github.com/Echtzeitsysteme/gips-tests/pull/38, test testMapSnodeFirstInvalid):

• Create a model that is in fact infeasible.
• Run api.buildILPProblem() and api.solve() -> The result shows that the validation log is invalid -> This is correct.
• Now reset the model and set up a feasible problem (e.g., by removing the blocking nodes in the graph).
• Run api.buildILPProblem() and api.solve() -> The result shows that the validation log is still invalid -> This is not correct.

(This bug also occurs vice versa, see test testMapSnodeSecondInvalid.)

[maxkratz]

Closed by https://github.com/Echtzeitsysteme/gips/pull/144.