Dotplot view can't be closed

Steps to reproduce:
1. Open "human_T1.fa"
2. Press "Build dotlpot" toolbar button
Expected state: "DotPlot" dialog appeared
3. Press "Ok" button in the dialog
Expected state: Dotplot view has appeared
4. Close dotplot view
Expected state: "Save dot-plot" dialog has appeared
5. Press "Yes" button
Expected state: the view has been closed
Current state: the view can't be closed