Actual behavior:
If the display view (render window) is closed and new data (DICOM data) is loaded (e.g. via drag'n'drop into the data manager), the QmitkImageNavigator receives a signal to update the status bar.
Since no render window is set before the display view reopens, MITK crashes.

Steps to reproduce:

• Open MITK and close the "Display" view
• Load an image file (e.g. .dcm or .nrrd) via drag 'n' drop or via "Open File"
• MITK crashes in 'void QmitkImageNavigatorView::UpdateStatusBar()'

Expected behavior:
The update should only happen after the render window (display) has been initialized automatically by the file loading process (when the image navigator holds a valid pointer to the current render window).