AlgorithmView clears the ViewType of the ProblemViewHost leaving the Viewhost in an invalid state

[mkommend]

When the problem of an algorithm is changed, the according AlgorithmView updates its content:

 protected virtual void Content_ProblemChanged(object sender, EventArgs e) {
      if (InvokeRequired)
        Invoke(new EventHandler(Content_ProblemChanged), sender, e);
      else {
        problemViewHost.ViewType = null;
        problemViewHost.Content = Content.Problem;
      }
    }

However, when the algorithm resets its problem to the previous value(for example when the new problem cannot be used in combination with the algorithm) OnContentChanged is not executed and the ViewType stays null. The correct problem is still displayed, but the ViewHost is in an invalid state (OnContentChanged is responsible for setting the correct ViewType if it is null) and exceptions occur when switching the views or opening them in another tab.

[mkommend]

r13560: Changed algorithmView to reset the viewType of the problemViewHost only when the types of the displayed and new problem differ.

[ascheibe]

Reviewed r13560, ok.

[mkommend]

r13955: Merged r13560 into stable.