ImageViewer: Fix and improve setting default attributes #176

Job	Run time
test / build (macOS-latest, 3.9, orange-oldest, 5.15., false) / orange-oldest macOS-latest py3.9 qt5.15.	2m 23s
test / build (macOS-latest, 3.10, orange-released, 6.6., false) / orange-released macOS-latest py3.10 qt6.6.	55s
test / build (macOS-latest, 3.11, orange-latest, 5.15., false) / orange-latest macOS-latest py3.11 qt5.15.	2m 30s
test / build (macOS-latest, 3.10, orange-released, 5.15., false) / orange-released macOS-latest py3.10 qt5.15.	2m 22s
test / build (ubuntu-latest, 3.10, orange-released, 6.6., false) / orange-released ubuntu-latest py3.10 qt6.6.	1m 45s
test / build (ubuntu-latest, 3.10, orange-released, 5.15., false) / orange-released ubuntu-latest py3.10 qt5.15.	2m 53s
test / build (ubuntu-latest, 3.11, orange-latest, 5.15., false) / orange-latest ubuntu-latest py3.11 qt5.15.	3m 43s
test / build (ubuntu-latest, 3.9, orange-oldest, 5.15., false) / orange-oldest ubuntu-latest py3.9 qt5.15.	2m 20s
test / build (windows-latest, 3.10, orange-released, 6.6., false) / orange-released windows-latest py3.10 qt6.6.	2m 38s
test / build (windows-latest, 3.10, orange-released, 5.15., false) / orange-released windows-latest py3.10 qt5.15.	3m 45s
test / build (windows-latest, 3.11, orange-latest, 5.15., false) / orange-latest windows-latest py3.11 qt5.15.	5m 26s
test / build (windows-latest, 3.9, orange-oldest, 5.15., false) / orange-oldest windows-latest py3.9 qt5.15.	3m 37s
	34m 17s

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