Closing current previewstream

[tonoizer]

Issue description

Describe your issue in detail here

When you close your current previewed application, nothing is displayed any more and additionally errors occur.
But in general, when you close an application while Vigad is running, errors are thrown!

• Prevent Errors thrown when applications in general are closed, refresh the screens of an applications etc.
• When the currently streamed application is closed, use the default Screen as the replacement

Definition Of Ready (DoR)

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• the issue is labeled
• the issue is assigned to the current sprint
• the issue is estimated
• a meaningful title has been set
• the issue is described in detail