fix: properly set list backgrounds when switching between lists

Probably caused by the blur hash feature, switching between lists would not work if the list background was set via unsplash. I've refactored the whole decision tree which checks if a background should be loaded or not. It actually does not matter where the background is from (unsplash or upload) or if we had one in the last list - we only need to know if the current list has a background or if we just changed it and need to update right away.

src/views/tasks/TaskDetailView.vue

@@ -520,7 +520,7 @@ export default defineComponent({
 			handler(parent) {
 				const parentList = parent !== null ? parent.list : null
 				if (parentList !== null) {
-					this.$store.commit(CURRENT_LIST, parentList)
+					this.$store.dispatch(CURRENT_LIST, {list: parentList})
 				}
 			},
 			immediate: true,