fix(ui): crash when closing a window with a pending notification
Description
Applications may crash when closing a window whereas a notification is displayed.
Steps to reproduce
On Windows:
- Launch SightViewer, with the default config (no dicom preference set - not sure that matters)
- Click on "Open PACS"
- Open the settings
- Click on "Ping PACS" (it should fail as it won't be properly configured)
- Close the settings
- Close the "PACS" Window
- crash
Proposal
Set an "empty" function for the close callback just before closing.
Functional specifications
It should not crash, notification should be deleted properly.
Test plan
Follow instruction of the crash test above.