Fix inability to edit multiple categories

Twigs/Category/CategoryDataStore.swift

@@ -100,6 +100,10 @@ class CategoryDataStore: ObservableObject {
             })
     }
     
+    func clearSelectedCategory() {
+        self.category = .failure(.unknown)
+    }
+    
     private let categoryRepository: CategoryRepository
     init(_ categoryRepository: CategoryRepository) {
         self.categoryRepository = categoryRepository

Twigs/Category/CategoryFormSheet.swift

@@ -78,6 +78,8 @@ struct CategoryFormSheet: View {
                             archived: false
                         ))
                     })
+        }.onDisappear {
+            self.categoryDataStore.clearSelectedCategory()
         }
     }