Add missing invalidateCache in N/B Voltage Level

[sebalaig]

• Do you want to request a feature or report a bug?
  Bug fix
  Add missing invalidateCache in N/B Voltage Level powsybl-core#1710

• What is the current behavior?

• If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem
  The following program crashes:

powsybl::iidm::Network network("test", "test");
        powsybl::iidm::Substation& substation = network.newSubstation()
                                                 .setId("S1")
                                                 .setCountry(powsybl::iidm::Country::FR)
                                                 .setTso("TSO")
                                                 .add();
        powsybl::iidm::VoltageLevel& vl1 = substation.newVoltageLevel()
                                             .setId("VL1")
                                             .setTopologyKind(powsybl::iidm::TopologyKind::NODE_BREAKER)
                                             .setNominalV(90.0)
                                             .setLowVoltageLimit(88.0)
                                             .setHighVoltageLimit(96.0)
                                             .add();

        powsybl::iidm::BusbarSection& bbs1 = vl1.getNodeBreakerView().newBusbarSection()
                                                                     .setId("BBS1")
                                                                     .setName("BBS1_NAME")
                                                                     .setNode(0)
                                                                     .add();

      const auto& bus1 = bbs1.getTerminal().getBusView().getBus();
      if (bus1) {
        bus1.get().setV(3).setAngle(4);
      }
      else {
        std::cerr << "bus1 is null" << std::endl;
      }

      powsybl::iidm::BusbarSection& bbs2 = vl1.getNodeBreakerView().newBusbarSection()
                                                                   .setId("BBS2")
                                                                   .setName("BBS2_NAME")
                                                                   .setNode(1)
                                                                   .add();

      const auto& bus2 = bbs2.getTerminal().getBusView().getBus();  // <-- crash here
      if (bus2) {
        bus2.get().setV(3).setAngle(4);
      }
      else {
        std::cerr << "bus2 is null" << std::endl;
      }

• What is the expected behavior?

• What is the motivation / use case for changing the behavior?

• Please tell us about your environment:

  • PowSyBl Version: ...
  • OS Version: ...

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, spectrum, etc)

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