Disconnect simulator plugin signals before unloading

When we unload a simulator plugin, we don't need to listen to any
of its events anymore. Therefore disconnect its signals before
unloading.
The disconnect already existing before this commit probably had the
same intention but did the wrong thing.

refs #801

src/blackcore/context/contextsimulatorimpl.cpp

@@ -484,8 +484,8 @@ namespace BlackCore
                 if (sim)
                 {
                     // disconnect signals and delete
+                    sim->disconnect(this);
                     sim->unload();
-                    this->disconnect(sim);
                     sim->deleteLater();
                     emit simulatorPluginChanged(CSimulatorPluginInfo());
                 }
@@ -611,8 +611,6 @@ namespace BlackCore
 
         void CContextSimulator::restoreSimulatorPlugins()
         {
-            //! \todo #801, this shutdown flag should not be required
-            if (this->getRuntime()->isShuttingDown()) { return; }
             stopSimulatorListeners();
 
             auto enabledSimulators = m_enabledSimulators.getThreadLocal();